Wormlike Perovskite Oxide Coupled with Phase‐Change Material for All‐Weather Solar Evaporation and Thermal Storage Applications

Abstract

Interfacial solar‐driven water evaporation has shown promising prospects in desalination technology. However, the lower photothermal conversion efficiency caused by the intermittent nature of sunlight and salt accumulation remains a significant challenge for continuous desalination. Herein, the hierarchical design of interfacial solar evaporation is reported, which realizes enhanced photothermal conversion, waste heat storage/release, and effective thermal management for continuous desalination. The solar evaporator is composed of worm‐like SrCoO₃ perovskite oxide anchored on super hydrophilic polyurethane (PU) foam succeeded by in situ polymerization of conducting polypyrrole (SrCoO₃@PPy). The energy storage system is introduced within polyurethane matrix by a paraffin block followed by a tongue‐and‐groove structure for convective water transportation, and a heat recovery unit largely reduces heat losses. The solar evaporator possesses excellent evaporation rates (2.13 kg m⁻² h⁻¹) along with 93% solar‐to‐vapor conversion efficiency under 1 kw m⁻² solar irradiation owing to its minimum equivalent evaporation enthalpy and (0.85 kg m⁻² h⁻¹) under intermittent solar irradiation as compared to conventional solar evaporators. More importantly, state‐of‐the‐art experimental investigations validate waste heat recovery/release and the salt‐resistant capability of solar evaporators optimized by computational fluid dynamic simulation. This study breaks conventional solar interfacial evaporation's limitations and demonstrates stable desalination under intermittent sunlight.

Introduction

Nowadays, freshwater shortage is still one of the most serious crises in the world owing to human activities and environmental pollution.^[1] The world is suffering from severe freshwater scarcity as a result of excessive natural evaporation caused by global warming as a result of population increase, climate change, and pollution development over the last few decades.^[2] It is pressing to seek efficient, low-cost, and sustainable desalination technology. Solar-driven evaporation is a promising technology to desalinate seawater, wastewater treatment, and heating/cooling applications using solar energy, which is especially important for developing countries and remote areas lacking basic infrastructure.^[3] So far, initiatives and approaches have been made to achieve increased evaporation performance by optimizing a variety of parameters, that is, 1) prospective photothermal materials for broadband solar absorption with lower enthalpy, 2) Optimization of salt-resistant evaporation structures to simultaneously produce freshwater and enhanced exploitation of accumulated heat for vapor generation, and 3) integration of a condensing system for immediate collection of water, recycling of latent heat, and capturing water vapor in the air.^[4] However, because of the day/night cycle, most solar evaporator systems operate intermittently owing to the restricted light duration, which is particularly unfavorable for the sustained practical use of solar evaporators. Xu et al. reported a 3D hollow and compressible photothermal evaporator to harvest massive energy from both the surrounding air and bulk water, endowing an extremely high evaporation rate of (7.6 kg m⁻² h⁻¹) under 1.0 sun irradiation.^[5] Additionally, salt accumulation inevitably occurs during seawater desalination, severely restricting the evaporation efficiency due to clogged water channels and deterioration of the solar evaporator's surface.^[6] Thanks to the research community, a variety of hybrid evaporation structures are devised to address these pressing challenges, that is, 3D conductive evaporators to harvest additional energy other than solar light,^[7] nanofibers,^[8] bilayer Janus evaporators^[9] for effective salt-tolerant capability, and increased evaporation efficiency without affecting the water channels. Unfortunately, the rapid convection transmits photothermal heat to the surrounding environment and the sometimes perforations of the evaporator reduce the device's thermal conversion efficiency due to inevitable heat losses. Wani et al. also reported complex perovskites for enhanced solar-to-vapor conversion efficiencies, for example, LaNiO₃ and LaCoO₃, where the metallic nanostructure of LaNiO₃ endows higher photothermal conversion efficiency as compared to semiconductive LaCoO₃.^[10] Even with the advancement in nanoenabled photothermal materials and structural optimization for a variety of variables, there are some significant obstacles to further improving the photothermal conversion efficiency of the deemed solar evaporators.^[11] Of note, effective thermal management of novel evaporation structures equipped with salt-tolerant and superhydrophilic water channels should all be regulated simultaneously to devise hybrid solar evaporation systems for long-term efficacy under intermittent conditions.^[12]

To date, innumerable photothermal materials have been investigated, that is, semiconductors, metal nanoparticles, conductive polymers, and carbon-based materials to accomplish broadband solar absorption.^[12,13] Recently, perovskite oxides have caught extensive attention in driving solar evaporation performances as they show strong photothermal response, high stability, economic feasibility, and environmental friendliness.^[14] SrCoO₃ is a perovskite material in the form of ABO (A = alkaline earth metal and B = 3d transition metal) in which O 2s and 4p orbitals lie below the conduction bands and conduction bands arise from the hybridization of the Co 3d and O 2p orbitals. Due to their high oxygen permeation flux caused by the high levels of both ionic and electronic conductivities and enhanced catalytic activity, SrCoO₃ has been explored for diversified applications, that is, solar cells,^[15] sensors,^[16] electrolyzers,^[17] and thermochemical water-splitting reactors for H₂ production.^[18] Polymer-based semiconductive materials also offer a wide range of solar absorption due to their unique structure and hydrogen bonding within OH groups.^[19] Polypyrrole (PPy) is a semiconducting polymer that possessed a wide range of solar absorption attributed to its conjugated system and delocalization of electrons.^[20] Recent studies^[21] demonstrate how water molecules behave differently when exposed to hydrophilic polymeric networks owing to the strength of hydrogen bonds (−OH) than in the bulk state. These OH bonds share a similar structure in bulk water (BW) and free water (FW), while nonfreezing intermediate water (IW) contains impure water molecules in the physical interaction with the polymer backbone matrix that ends up in weak or fragile hydrogen bonding.^[22] This results in a high diffusivity of IW than FW and BW and ultimately leads to a fast evaporation rate.^[22]

Phase-change materials (PCMs) have gained outstanding attraction in energy storage applications, capable of absorbing and storing energy from an environmental heat source such as solar energy or waste heat and releasing the as-stored thermal energy via the phase–change process for multiple applications such as waste heat recovery, electricity generation, and building insulation, and so on.^[3,23] Taking advantage of the large heat storage capacity, excellent stability, small volume changes, as well as pollution-free properties, recently, organic PCMs are considered the most promising materials to overcome the intermittence of solar illumination and further, improve energy utilization by absorbing the solar energy in the daytime and releasing the energy in the nighttime.^[24] Hence, the combination of waste heat utilization and interface evaporation is a prospective strategy to optimize water evaporation performance.^[3] Among various PCMs, paraffin wax is acknowledged as the most efficient PCM owing to its applicability over a wide range of temperatures.^[25] Further, it can also freeze easily without undergoing supercooling and it has a relatively high heat of fusion which bestows it attributes of cost-effectiveness, feasibility, and extensive use.^[24,25]

Herein, we report the development of all-weather solar evaporators composed of wormlike SrCoO₃@PPy nanocomposite anchored on hydrophilic PU foam coupled with paraffin block followed by a tongue-and-groove structure for convective water transportation through PU wicks and a waste recovery unit that largely reduces heat losses, as compared to conventional solar evaporators. The SrCoO₃@PPy shows good solar absorption (94%) ensemble with a hydrophilic polyurethane substrate that provides an open porous assembly for quick water transport and vapor escape. Moreover, the conductive polymeric network of SrCoO₃@PPy has a greater influence on hydrogen bonding for different states of water such as bound, intermediate (IW), and FW states. As compared to conventional structures (Figure 1a₁), Xu et al.^[26] reported that the evaporation rate did not remain constant as the evaporation surface area increased. However, increasing the evaporation surface area reduced the actual evaporation rate.^[26] Inspired by recent progress in structural optimization, a new strategy to develop all-weather solar evaporation by removing a selective portion of the evaporation surface and the energy storage system is established within PU matrix by a paraffin block followed by a tongue-and-groove structure for convective water transportation, and a waste recovery unit largely reduces heat losses, as illustrated in Figure 1a₂. The developed solar evaporator possesses excellent evaporation rates (2.13 kg m⁻² h⁻¹) under 1 kw m⁻² and effectively recovers the energy being conducted toward the downward matrix and overcomes the limitation of evaporation structure (0.85 kg m⁻² h⁻¹) under intermittent solar irradiation (stored PCM energy). The all-weather solar evaporator performed better under different environmental conditions, for example, humidity or temperature.

[IMAGE OMITTED. SEE PDF]

The long-term evaporation endows excellent yield (14.96 kg m⁻²) under one sun for consecutive 8 hrs. More importantly, state-of-the-art experiments validate waste heat recovery/release and the salt-resistant capability of solar evaporators optimized by computational fluid dynamic (CFD) simulation. Hence, this strategy benefits in terms of all-weather functioning potential along with a multidirectional mass transfer mechanism to prevent surface aching and sustained long-term stability when operated under intense seawater conditions.

Results & Discussion

The facile synthesis of wormlike SrCoO₃ perovskite oxide was successfully carried out using the sol–gel technique, as schematically illustrated in Figure 2a. For this, the following precursors were dissolved evenly in a prepared solution (Section 4.2) using a magnetic stirrer at 260 °C continuously until the formation of a homogeneous gel. Subsequently, the obtained gel was dried at 200 °C and dark-gray powder of wormlike SrCoO₃ was obtained after grinding. The obtained powder was calcined at 1000 °C. The synthesized wormlike SrCoO₃ perovskite oxide was utilized for the fabrication of the photothermal layer. The detailed characterization tools of synthesized wormlike SrCoO₃ perovskite oxide are described in Note S1, Supporting Information. Figure 2b schematically illustrates the integration of an all-weather solar evaporator by the introduction of paraffin wax as a PCM unit. Paraffin wax is an organic colorless material composed of a complex mixture of hydrocarbon derivatives in the form of a straight chain ranging from ≈C₂₀–C₃₀ with a formula CH₃ (CH₂)_n CH₃, where n ≥ 18.^[25] It exists in the form of a crystal structure and is preferred over other PCMs because it is nonreactive, nontoxic, has low melting point, and is economically feasible.^[25] In the second step, the prepared perovskite SrCoO₃ was mixed in the terpineol binder to form a homogeneous slurry which was anchored on the surface of the polyurethane foam (PU) crafted in the form of wicks by physical coating using a BOSOBO paintbrush. Polyurethane foam is a linear polymer composed of organic units joined by links of carbamate with the chemical formula C₂₇H₃₆N₂O₁₀.^[27] Basically, urethane is a carbonyl-containing functional group in which the carbonyl carbon is bonded to both an OR group and an NR₂ group, forming a ring-like structure containing a linear chain.^[27] Due to its open porous structure, low cost, and thermal insulation properties, PU foam is selected as a potential hydrophilic substrate. For in situ polymerization, the wormlike SrCoO₃ coated PU foam was placed in an oven at 80 °C for 2 h to dry the coating and then sprayed with preprepared two solutions, e.g., initiators and monomer solutions. Eventually, some selected portions of the interfacial surface were removed to enhance the evaporation rate and regulate the self-regeneration system with the insertion of PCM in the space between adjacent PU wicks to develop an integrated all-weather solar evaporation system.

[IMAGE OMITTED. SEE PDF]

The self-regenerating design effectively localizes the heat accumulation while the convective PU wicks promote continuous water transport and efficient salt tolerance during continuous evaporation. Figure 2c represents the Fourier-transform infrared spectroscopy (FTIR) spectrum of SrCoO₃@PPy. The metal oxide (SrO, CoO) is observed in different modes of vibration. CoO is observed to have two vibrational modes corresponding to Co²⁺ and Co³⁺ valence, revealing an asymmetric stretching vibrational mode, which is attributed to peaks appearing at 543.42 and 587.70 cm⁻¹. However, the bands appearing at 985.05 and 1144.13 cm⁻¹ occur due to the stretching of SrO-type metal oxide vibrational modes.^[16] The bands at 1427.28 and 1561.71 cm⁻¹ are attributed to the fundamental vibrations of the polypyrrole ring, due to the CH in-plane vibrations, and that at 856.20 cm⁻¹ is due to the CH out-of-plane vibration.^[28] The peak at 1715.21 cm⁻¹ indicates the existence of OH bonding of FW molecules in SrCoO₃@PPy. The broad band identified at 2837.49 cm⁻¹ and 3200.18 cm⁻¹ signifies the stretching vibrational mode of OH bonding. Further, the elemental and chemical composition of the perovskite material SrCoO₃ was investigated by X-ray photoelectron spectroscopy (XPS). The full XPS scan of SrCoO₃ is demonstrated in Figure S1a, Supporting Information, revealing the presence of Sr 3d, Sr 3p, C 1s, O 1s, and Co 2p, respectively. The high-resolution spectrum of the Sr 3d core-level spectrum is shown in Figure 2d, which is deconvoluted into four subpeaks appearing at 133.23, 132.62, 134.43, and 134.78 eV, respectively. The peaks at 133.23 and 134.78 eV binding energies correspond to Sr 3d_5/2 and Sr 3d_3/2 of Sr²⁺, respectively, whereas the appearance of the peaks at 132.62 eV and 134.43 eV is due to the binding energies of Sr—O and SrCO₃ bonds, respectively. From Figure 2e, the Co 2p spectrum is decomposed into two distinct peaks and three weak peaks. The two spin-orbit doublets assigned to cobalt oxides located at 780.02 and 795.04 eV can correspond to Co 2p (1/2) and Co2p (3/2), respectively. The spin-orbit doublet of Co 2p (1/2) can be deconvoluted into three peaks at 782.54, 780.48, and 779.84 eV, which are attributed to Co³⁺ 2p (1/2) and Co²⁺ 2p (1/2) configurations, respectively. The Co 2p (3/2) spin-orbit doublet can also be deconvoluted into two distinct peaks located at binding energies of 796.05 and 794.90 eV and are assigned to Co³⁺ 2p (3/2) and Co²⁺ 2p (3/2), respectively. However the full XPS scan, and O 1s, C1s, and Sr 3p are demonstrated in Figure S1a–d, Supporting Information.

Raman spectroscopy was performed to insight the lattice vibrations that correspond to the perovskite SrCoO₃ and in situ-polymerized SrCoO₃@PPy composite and recorded results are demonstrated in Figure 2f. The first four peaks appearing at 130, 652, 938, and 992 cm⁻¹ define the features and lattice vibrations of perovskite SrCoO₃, as reported in the literature.^[17] The broad peaks appearing at 1374 and 1599 cm⁻¹ correspond to the CH ring deformation vibration of PPy. The peak at 1374 cm⁻¹ is attributed to the in-plane CC and CH stretching vibrations whereas the second peaks at 1599 cm⁻¹ show the CC symmetric and CC asymmetric vibrations, revealing the successfully controlled in situ polymerization of SrCoO₃ and formation of the polymeric network.

The microstructure and morphologies of the prepared wormlike SrCoO₃ perovskite oxide, hydrophilic PU foam, SrCoO₃-coated PU foam, and in situ-polymerized SrCoO₃@PPy/PU foam were analyzed by advanced field-emission scanning electron microscopy (FESEM). Figure 3a–c represents the FESEM images of the SrCoO₃ perovskite oxide, delineating that hierarchical SrCoO₃ possesses a dense and closely distributed wormlike structure with an approximate diameter of 15 nm. The randomly distributed wormlike structure with a rough and diffusive surface may contribute toward excellent solar absorption with minimum reflection. Figure 3d shows the FESEM image of polyurethane foam, featuring the extended network of open pores, which are interconnected both horizontally and vertically with the specific diameter and promote quick water transport and facile vapor escape. The selection of the water transport substrate plays a decisive role in incorporating all parameters in a single evaporation structure, for example, hydrophilicity, salt resistance, effective thermal management, and antifragile nature.^[1,29–32] The horizontally interconnected channels are crucial for horizontal mass transfer via salinity gradient.^[32] Figure 3e demonstrates the cross-sectional image of SrCoO₃-coated PU foam, showing homogeneous coating with a thickness of ≈417.8 μm. Figure 3f shows the surface view of SrCoO₃-coated PU foam, manifesting homogeneous deposition over hydrophilic channels and imparting its rough texture to enhance solar absorption and better thermal localization. However, the in situ-polymerized SrCoO₃@PPy anchored on PU foam could be seen in the cross-sectional view, as illustrated in Figure 3g.

[IMAGE OMITTED. SEE PDF]

It depicts the denser layer of PPy over SrCoO₃@PU foam, revealing a total thickness of 963.6 μm (PPy coating = 963.6–417.8 = 545.8 μm). Figure 3h demonstrates the surface view of SrCoO₃@PPy, which shows a more porous and diffuse texture for enhanced light capturing and excellent wettability of semiconductive PPy due to π-conjugated electron systems^[28] and enhanced solar absorption by inducing multiple incident rays within the matrix. Furthermore, the energy-dispersive spectrometry (EDS) mapping of SrCoO₃@PPy anchored on PU foam is also investigated (Figure S2, Supporting Information), confirming the in situ polymerization and elemental presence of Sr, Co, N, C, and O.

Broadband solar spectral-capturing potential and high absorption capability are crucial factors for enhanced solar-to-thermal conversion efficiency.^[33] The solar absorption of PU foam, SrCoO₃, and SrCoO₃@PPy was examined by ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy across the entire range (200–2500 nm) to inspect the comparative absorption potential, and obtained results are shown in Figure 4a. As obvious, the average absorption of the PU foam is around 50% with slight fluctuation over the complete solar spectral length. The absorption of wormlike SrCoO₃ perovskite oxide and SrCoO₃@PPy solar evaporator is significantly higher than PU substrate due to its enhanced reflection (white color). The SrCoO₃@PPy composite is observed to manifest maximum solar absorption up to 95% with a minimum reflection due to its porous and diffused texture. This distinct solar absorption is attributed to the effective capturing of incident light due to rough surface texture coupled with a localized π-conjugated electronic system of PPy,^[28] facilitating the enhanced absorption of wormlike SrCoO₃ perovskite oxide for effective solar-to-thermal conversion efficiencies of solar-driven interfacial systems. Further, photothermal conversion behavior was assessed by a change in surface temperature using an IR camera. For this, the surface temperatures of pure water, PU foam, SrCoO₃@PU, and SrCoO₃@PPy/PU under 1 kW m⁻² solar irradiation for 20 min to inspect the real-time variations and captured images are shown in Figure 4b. As obvious, the temperature of SrCoO₃@PPy/PU quickly rises to 41.2 °C within 20 min, demonstrating the rapid response of the enhanced photothermal conversion process. In comparison, the temperature of pure water would only increase by 26 °C within 10 min under the same solar irradiation. The combined effect of the anisotropic lower thermal conductivity of SrCoO₃@PPy/PU is more conducive to the formation of “thermal localization” during evaporation. These results indicate that SrCoO₃@PPy/PU has good application prospects in photothermal conversion. The practical performance of any solar evaporator device is largely influenced by its absorption and hydrophilicity.^[34] During the integration of multiple applications, these factors are of utmost importance and are to be considered critically.^[35] The hydrophilicity PU, SrCoO₃@PU, and SrCoO₃@PPy/PU was checked by a water contact angle test and captured images are shown in Figure 4c. As shown, due to the open microporous well-aligned assembly of PU foam, the water droplet gets fully saturated in 0.01 s in all three systems, revealing the sustainment of the hydrophilicity of PU after the coating of SrCoO₃/PU and SrCoO₃@PPy, which perfectly manages the water uptake to the interfacial layer and promotes quick vapor release. The SrCoO₃@PPy exhibits excellent wetting properties due to its porous polymeric network. In addition, the interconnected water channels are crucial to prevent heat losses as the thermal conductivity of PU is less than water. For this, we also investigated the thermal conductivities of PU foam, SrCoO₃/PU, and SrCoO₃@PPy/PU in both dry and wet states, and measured conductivities are demonstrated in Figure 4d. The thermal conductivity of the dry SrCoO₃@PPy was found to be 0.0613 W m⁻¹ K⁻¹, which is much lower compared to water (0.600 W m⁻¹ K⁻¹). However in the hydrated state, the SrCoO₃@PPy is invariable; thus, the thermal conductivity of the fully saturated SrCoO₃@PPy is merely 0.0921 W m⁻¹ K⁻¹, which is still much lower than pure water's conductivity, as illustrated in Figure S3a,b, Supporting Information. The experiment details and calculations of the obtained thermal conductivities are described in Note S2, Supporting Information. Hence, the broadband solar absorption and excellent hydrophilicity with minimum thermal conduction of SrCoO₃@PPy solar evaporator pave the path for its tremendous potential toward practical applicability to meet heat loss challenges.

[IMAGE OMITTED. SEE PDF]

The evaporation rate of a solar evaporator is comprehended by the existence of individual water molecules or fragmented water clusters at the liquid–air interface.^[36] Hence, the intense solar absorption and heat confinement at the interfacial layer can efficaciously drift the smooth vapor generation at the air–liquid interface.^[37] The broadband solar absorption along with the minimum thermal conductivity of the all-weather SrCoO₃@PPy solar evaporator facilitates excellent confinement of thermal energy at the interfacial layer. Figure 5a schematically illustrates the interfacial evaporation strategy, water molecules’ interaction in a polymeric network, and self-regenerating system for all-weather solar evaporation under intermittent solar irradiation via the PCM unit. More importantly, water molecules behave differently in a polymeric network. Yu et al.^[22] first time reported this behavior in the hydratable skeleton of polypyrrole. According to this recent progress,^[19] the water molecules in a hydrated polymeric network may be classified into three types: FW, IW, and bound water (BW), respectively. Nonfreezing or BW refers to those water molecules which are bonded by hydrogen bonds located on specific sites of the polymer chains. However, the IW comprises the development of a secondary or tertiary hydration shell around the BW, which experiences nonhydrogen or weak bonds from the polymer chains due to the presence of N³⁻ in PPy chains.^[28]

[IMAGE OMITTED. SEE PDF]

Upon the further increment of the water content in the system, the FW's availability is increased, which is structurally identical to BW. Indeed, the BW experiences a comparatively strong bonding force and hence low mobility and it needs high energy for evaporation.^[22] In comparison, the diffusivity of the IW is higher than BW and FW, providing SrCoO₃@PPy with highly drifted water transport occupied by weakly bonded IW which evaporates at the air–liquid interface and providing enhanced solar-to-vapor conversion efficiency. To further evaluate the phenomena, the Raman spectra of the −OH stretching in the hydrogen bonding region were used to inspect the water states in SrCoO₃@PPy, as shown in Figure 5b. The OH stretching of water molecules and the −OH peaks of the adsorbed water molecules in the hydrated SrCoO₃@PPy could be classified into two types: the in-phase and out-of-phase − OH stretching with FW vibration exhibiting two typical hydrogen bonds at 3205 and 3340 cm⁻¹, respectively.

Further, the bands located at 3455 and 3617 cm⁻¹ can be attributed to the weak hydrogen-bonded IW with the symmetric and asymmetric −OH stretching modes, respectively. However, the strong peaks of the IW show that SrCoO₃@PPy is equipped with the maximum amount of IW. These phenomena substantiate the existence of IW content in the hydrated SrCoO₃@PPy matrix for enhanced evaporation, which was affirmed by quantifying the water concentration or swelling ratio (Q_s) for the PU foam, SrCoO₃/PU, and SrCoO₃@PPy using the following equation.^[38]1$Q_{\mathrm{s}}=\frac{W}{W_{\mathrm{d}}}$where W and W_d denote the weight of a fully saturated and dried system, respectively. The obtained results are demonstrated in Figure 5c, revealing the maximum swelling capability of SrCoO₃@PPy to transport water under ambient conditions attributed to the presence of hydratable−NH₂ and −OH groups in the polymeric chains of SrCoO₃@PPy. The observed phenomena give insights into the new developments in the perovskite oxide and its polymeric network to explore the different states of water molecules based on weak or strong interaction of hydrogen bonding, especially in solar-driven water-splitting applications.

Figure 6a demonstrates the schematic illustration of the facile setup of an all-weather solar evaporation setup including a paraffin block as a heat storage/release unit along with holes consisting of the in situ-polymerized SrCoO₃@PPy photothermal layer for seawater desalination under solar irradiance and intermittent conditions. Herein, the following solar evaporation systems were examined and their surface temperatures analyzed, for example, bulk seawater, PU foam, PPy-coated PU foam, wormlike SrCoO₃-coated PU foam, and in situ-polymerized SrCoO₃@PU foam (SrCoO₃@PPy) under 1 sun during 1 h continuous evaporation with the help of thermocouples embedded on the targeted surfaces. The SrCoO₃@PPy achieved maximum temperature (41.1 °C) as compared to other evaporation systems such as PU (31.8 °C), PPy@PU (37.6 °C), and SrCoO₃@PU (39.5 °C), as illustrated in Figure 6b. However, the surface temperature of the all-weather SrCoO₃@PPy solar evaporator was also examined under different solar irradiation up to 3 sun or 3 kW m⁻², as shown in Figure 6c. As expected, the solar evaporator exhibited enhanced surface temperature (58.27 °C) under 3 kW m⁻², validating its light-dependent photothermal response. Moreover, the reproducibility test of the developed enhanced surface temperature was also examined and demonstrated in Figure S4, Supporting Information. The surface temperatures of the paraffin wax under multiple solar intensities up to 3 kW m⁻² were also recorded, as illustrated in Figure S5, Supporting Information. The water evaporation rate of developed solar evaporators was also investigated under similar conditions, under 1 kW m⁻² solar intensity, excluding dark conditions, as shown in Figure 6d. The SrCoO₃@PPy solar evaporator achieved the maximum evaporation rates coupled with (2.13 kg m⁻² h⁻¹) and without PCM unit (1.96 kg m⁻² h⁻¹), as compared to other solar evaporators such as BW (0.11 kg m⁻² h⁻¹), PU foam (0.6 kg m⁻² h⁻¹), PPy@PU (1.44 kg m⁻² h⁻¹), and SrCoO₃@PU (1.70 kg m⁻² h⁻¹) under 1 sun. As reported, for larger evaporation areas, the convection is unable to efficiently extend to the middle of the interfacial layer where a “dead evaporation zone” is created.^[26] Considering this fact, the removal of this dead evaporation can lead to the accomplishment of a higher evaporation rate using less photothermal material and ultimately leads to a high evaporation rate and also promotes the self-regenerating potential for salt rejection. In addition, the incorporation of the waste heat energy-storing unit (PCM) effectively recovers the waste energy lost during conduction and stores it in liquid form, while this heat is released and recovered when the PCM changes its form from liquid to solid.^[26] Under solar irradiation, an all-weather SrCoO₃@PPy solar evaporator efficiently transforms solar energy into thermal energy, which is mainly used to maintain water evaporation while the rest energy is stored in PCM (liquid phase) as waste heat.^[24] In the absence of light, the stored heat energy is released and diffused to the surface of the interfacial layer of the solar evaporator to maintain the surface temperature, improving solar energy exploitation and water evaporation efficiency. Figure 6e reveals the significant difference in temperature change during water evaporation for three heating–cooling cycles under 1 h light exposure and 10 min after the light is turned off. These results are also compared with the conventional SrCoO₃@PPy interfacial evaporation system without holes and PCM unit. Under solar illumination, no significant difference is observed between the temperature rise curve of the conventional system and our new system while the new system maintained a temperature for 60 min, which is a little higher than the conventional system. More importantly, after the solar simulator is turned off, a slower rate of temperature decline is observed in each cycle in the new system, resulting in a higher final temperature of about 28.08 °C, compared with 24.62 °C in the conventional interfacial evaporation system (Figure 6e). The developed all-weather solar evaporation system manifests improved photothermal response and thermal insulation, which is facilitated by the release of thermal energy from the phase-change process of the PCM.^[25]

[IMAGE OMITTED. SEE PDF]

Similarly, the evaporation rates of the conventional SrCoO₃@PPy (plain) and all-weather SrCoO₃@PPy/PCM (hole) solar evaporators were recorded for three consecutive cycles under 1 kW m⁻² solar irradiation and obtained graphs are shown in Figure 6f. The evaporation rates of pure water, SrCoO_3, and SrCoO₃@PPy were measured in the dark and corresponding enthalpies were carefully calculated using the following equation.^[37]2$E_{\text{equ}}{m}_1=E_{\mathrm{w}}{m}_{\mathrm{w}}$where $E_{\text{equ}}$ is the equivalent of evaporation enthalpy and $m_1$ is the mass change of the water over the SrCoO₃@PPy evaporator. $E_{\mathrm{w}}$ and $m_{\mathrm{w}}$ represent the evaporation enthalpy and the mass change of the pure water during evaporation. Similarly, the equivalent enthalpy of SrCoO₃ was measured, as illustrated in Figure S6, Supporting Information. The SrCoO₃@PPy has the lowest equivalent evaporation enthalpy due to the weak intermolecular interaction of IW in the polymeric network of PPy, which significantly reduces the evaporation enthalpy. Hence, less energy is required to vaporize the same water content, which results in higher evaporation rates. The equivalent water vaporization enthalpies for water, SrCoO₃, and SrCoO₃@PPy were calculated to be 2260, 1506, and 1189 Jg⁻¹, respectively. The minimum equivalent evaporation enthalpy of SrCoO₃@PPy enables high IW content and a high evaporation rate. Under solar irradiations, the evaporation rate of the SrCoO₃@PPy/PCM (hole) is up to 2.13 kg m⁻² h⁻¹, which is reduced to 0.85 kg m⁻² h⁻¹ after turning off light using the stored thermal energy of the PCM unit. the conventional system achieved 1.89 kg m⁻² h⁻¹, which is reduced to 0.5 kg m⁻² h⁻¹ after turning off the light. Figure S7, Supporting Information, demonstrates the difference in evaporation rates of both conventional and all-weather solar evaporators with a difference of 0.27 kg m⁻² h⁻¹. Additionally, the consistency and long-term sustainability of the all-weather solar evaporator were checked by performing continuous evaporation cycles, as shown in Figure 6g, revealing the stable evaporation rate over 15 evaporation cycles with a negligible discrepancy in the evaporation rates, confirming excellent stability and the long-term durability of the all-weather solar evaporation system. Indeed, the air's relative humidity can also influence the evaporation rate of the solar evaporator. To assess the impact of the relative humidity, SrCoO₃@PPy was operated under different environmental conditions (temperature and humidity) and obtained results are shown in Figure S8, Supporting Information. A decrease in evaporation rate is observed with the increase of the relative humidity. It illustrates that high relative humidity in the environment could depress the rate of vapor diffusing from the interfacial surface to the ambient air, which ultimately reduces the evaporation rate. Furthermore, the long-term evaporation test was also performed for an all-weather solar evaporator to analyze the evaporation rate stability. Figure S9, Supporting Information, demonstrates the long-term performance for consecutive 8 h under 1 sun, which endows excellent mass change (14.96 kg m⁻²) without any surface deterioration or PCM leakage. The PCM leakage was controlled by a glass cavity which is filled with paraffin and encapsulated within the PU matrix. More importantly, the presented all-weather SrCoO₃@PPy/PCM (hole) solar evaporator exhibits a superior evaporation rate (2.13 kg m⁻² h⁻¹) and solar-to-vapor conversion efficiency (93%) as compared to previously reported solar evaporators,^[39,40] as illustrated in Figure 6h. The detailed solar-to-vapor conversion efficiency calculation is explained in Note S3, Supporting Information.

Seawater contains a high concentration of the primary salt ion, that is, 3.5 wt% which tends to accumulate inside the water channels in solar evaporating structures during consistent evaporation under intense seawater conditions.^[41] The salt-tolerance performance of the all-weather solar evaporator was evaluated by operating it against primary salt ions present in the seawater (3.5 wt%).^[41] The concentration of four primary salt ions (Na⁺, K⁺, Ca²⁺, Mg²⁺) was recorded in stimulated seawater and freshwater yielded after evaporation using inductively coupled plasma–optical emission spectrometry (ICP–OES), and obtained outcomes are shown in Figure 6i. However, a significant decrease in the concentration of salt ions by 3–4 orders of magnitude after desalination is observed, and much lower than the standard of drinking water which is set by the World Health Organization (WHO) and the US Environmental Protection Agency.^[1] Hence, the developed all-weather solar evaporator perfectly yields freshwater, which meets the quality of drinking water and promotes its applicability at the industrial level.^[28]

Salt accumulation occurs on the photothermal layer and blocks water transport channels during continuous solar evaporation under seawater conditions (3.5 wt%). This dilemma causes surface fouling and affects solar-to-vapor conversion efficiency.^[2] The developed all-weather evaporator exhibits self-regenerating convective wicks for continuous water transport through an open porous assembly, and the dead evaporation area was removed (holes), which was filled with a paraffin block, promoting hot brine via the salinity gradient to avoid salt accumulation within PU matrix due to stored thermal energy, as schematically illustrated in Figure 7a. Thus, the concentration gradient stimulates the continual salt exchange through microporous assembly in different concentration areas to reach an equilibrium state. Consequently, the excessive salt migrated toward convective wicks and dissolved back into the underlying water.

[IMAGE OMITTED. SEE PDF]

Hence, this strategy benefits the multidirectional mass transfer mechanism to prevent surface aching and sustained long-term stability along with enhancement of evaporation rate via the “more from less” strategy when operated under intense seawater conditions and promoted smooth evaporation rates.

Herein, a theoretically developed model coupled with experimented results can play a decisive role in better understanding of the salt rejection through convective wicks, for example, the simulated results of concentrated hot brine regulating from the top surface of the all-weather solar evaporator to underlying seawater via a salinity gradient potential. For this, the time-dependent computational fluid dynamics (CFD) simulation model^[42,43] has been established, which successfully shows insights into the downward migration of hot brine flux from the top interfacial layer through the localized wicks under experimental conditions. The corresponding numerical solution using the continuity equation^[42] is given in Note S4, Supporting Information, which resolves all the factors using momentum, energy, and salt flow assuming the chemical convection phenomena given in Equation (3) and (4) (Experimental Section). The simulated mesh geometry is based on the actual dimension of convective wicks meshed, as demonstrated in Figure S10, Supporting Information. Figure 7b shows the CFD simulation of a single wick with volume 0.5 cm × 0.5 cm × 2 cm = 0.5 cm³ with the mass flux of NaCl (1.5 g) migrating downward via laminar flow, that is, entering from the top which gradually dissolves to the water via salinity gradient potential. The developed convective wick geometry sets the side walls under no flux conditions to facilitate the 1D flow corresponding to the actual experimental setup. The time-dependent mass flow of the brine through these convective wicks is plotted for different time intervals showing the corresponding flow and concentration via steady-state laminar flow, revealing the decreased concentration and high dissolution of NaCl in water while migrating downward. The corresponding experimental investigations were also performed to witness actual salt rejection and self-regeneration potential through the localized wicks of the developed all-weather solar evaporator, as shown in Figure 7c. For this, 1.5 g solid NaCl powder was placed over the top surface of the all-weather solar evaporator and operated under 1 kW m⁻² solar intensity using stimulated seawater. The time-dependent salt rejection performance of our so-fabricated solar evaporator, where solid NaCl powder dissolved during continuous vapor generation and completely rejected from the top surface in continuous solar evaporation (210 min.) under 1 kW m⁻² solar intensity. Hence, the theoretical CFD model coupled with experimental proof successfully validates our prepared device as a self-regenerating and sustainable system with excellent hydrophilicity due to an interconnected highly open porous network which can potentially promote the superwetting property for quick water transport and vapor escape. In addition, the high solar efficiency is derived from the reuse of energy lost during evaporation by PCMs. The all-weather solar evaporator exhibits efficient photothermal conversion, fast water transfer, vapor spillage, and reasonable waste heat storage and releases, overcoming intermittent solar energy and thus improving overall energy efficiency. The system constructed in this work provides a promising solution for environmentally friendly, efficient, and sustainable freshwater production.

Conclusion

In summary, we have reported the multifunctional integration of wormlike SrCoO₃ into all-weather solar evaporation systems to overcome the limitations of the intermittent nature of solar in desalination technology, which realizes enhanced photothermal conversion efficiency (93%), waste heat storage/release, and effective thermal management for continuous desalination. The so-fabricated solar steam generator possesses excellent evaporation rates (2.13 kg m⁻² h⁻¹) under 1 kw m⁻², and (0.85 kg m⁻² h⁻¹) under intermittent solar irradiation (light off) using PCM stored energy as compared to conventional solar evaporators. The long-term solar-driven evaporation performance for consecutive 8 h under one sun, which endows excellent mass change (14.96 kg m⁻²) without any surface deterioration or PCM leakage. Of note, state-of-the-art experiments validate waste heat recovery/release and the salt-resistant capability of solar evaporators optimized by CFD simulation. The reported study also investigated the different water states in the polymeric network of the in situ-polymerized wormlike SrCoO₃@PPy network. The all-weather solar evaporator exhibits efficient vapor spillage and reasonable waste heat storage and releases, thus improving overall energy efficiency. The system constructed in this work provides a promising solution for environmentally friendly, efficient, and sustainable freshwater production.

Experimental Section

Materials

All synthetic chemicals strontium nitrate (Sr(NO₃)₂), cobalt nitrate (Co(NO₃)₂·6H₂O), iron nitrate (Fe(NO₃)₃·9H₂O), and ammonium hydroxide (NH₄OH) were used. Citric acid (C₆H₈O₇), phytic acid (C₆H₁₈O₂₄P₆), paraffin (C_nH_2n+2), and ethylenediaminetetraacetic acid (EDTA) were bought from the BASF Chemical Industries Co, Ltd., Wuhan. Ammonium persulfate (MnSO₄.4H₂O), pyrrole (C₄H₅N), spray water cans, and ethanol (C₂H₅OH) were purchased from Sinopharm Chemical Reagent Co. Ltd. Beijing, China. All the chemicals sustained a 99% purity level and proceeded without further purification, while deionized water was used for the experimental process.

Synthesis of Wormlike SrCoO₃ Perovskite Oxide

Wormlike SrCoO₃ perovskite oxide was prepared using the sol–gel technique. For this, fixed amounts of cobalt nitrate (Co(NO₃)₂·6H₂O), strontium nitrate (Sr(NO₃)₂), and iron nitrate (Fe(NO₃)₃·9H₂O) were dissolved into a solution containing ethylenediaminetetraacetic acid (EDTA), citric acid (C₆H₈O₇), and ammonium hydroxide (NH₄OH). The resulting mixture was heated at 260 °C for several hours while stirring continuously until the formation of a homogeneous gel. The obtained gel was dried in the oven at 200 °C and then ground to get a fine powder. Afterward, wormlike SrCoO₃ powder was calcinated at a high temperature (1000 °C) for 12 h in the presence of air.

In Situ Polymerization Process

In situ polymerization of conducting polypyrrole (PPy) was carried out using initiator and monomer solutions and these solutions were poured into spray cans. For the initiator solution, 2.74 g of ammonium persulfate was dissolved in 5 mL distilled water and stirred for 10 min without heating until the formation of a transparent solution (solution A). While pyrrole monomer was prepared, 0.84 mL pyrrole was dissolved in 5 mL isopropanol alcohol (IPA) followed by the addition of the 1.84 mL phytic acid (50%, wt% in water) and stirred for 10 min until the formation of a dark brown solution (solution B). Both initiator and monomer solutions were filled into spraying cans and saved for in situ polymerization of the conducting polypyrrole PPy.

Fabrication of SrCoO₃@PPy Solar Evaporator

The all-weather solar evaporator was fabricated by facile coating and in situ polymerization technique. The synthesized wormlike SrCoO₃ powder (1.5 g) was dissolved into a specific amount of volatile binder (terpineol, C₁₀H₁₈O) to form a homogeneous gel and coated on a hydrophilic polyurethane (PU) substrate using a paint brush. Initially, PU foam was crafted into a square shape (2 cm × 2 cm × 2 cm = 8 cm³) and the selected bottom part according to the tongue-and-groove structure for the convective water transport channels was removed. The two-phase wick geometry from the bottom surface with a specific area of 12.5% (0.5 cm × 0.5 cm × 2 cm = 0.5 cm³/single wick) assisted the localized water transport and the removing part of the bottom side was utilized for the PCM unit. The dried crafted SrCoO₃@PU was presented for the in situ polymerization of conducting polypyrrole (PPy). The same SrCoO₃ powder was anchored on a plain PU substrate without a PCM unit for better comparison. For this, the prepared initiator and monomer solutions were sprayed repeatedly (A then B) over the entire surface of SrCoO₃/polyurethane in A–B–A–B order until the surface achieved turned into a pitch-dark color with a uniform texture. The in situ polymerization of SrCoO₃/polyurethane (SrCoO₃@PPy) was confirmed when the solutions reacted with the surface and formed ultrablack coatings of conductive polymer along with an exothermic reaction. Eventually, a square-shaped glass filled with paraffin block was introduced in the space between two wicks as an energy storage unit to provide a 1D localized path for hot brine and water regulation. The individual SrCoO₃ powder was anchored on a plain PU substrate and in situ polymerization of PPy over PU without a PCM unit was also fabricated for better comparison. The overall fabrication was facile, reproducible, easy to install, and standalone for use in remote areas.

In Situ Solar-Driven Freshwater Setup

An interfacial solar-driven evaporation experiment was carried out through a solar simulator (PLS-FX300HU) equipped with a standard 1.5 G AM optical filter using various simulated solar intensities. The solar vapor generation device was installed in a beaker containing seawater, which was set on an advanced electronic balance with an accuracy of 0.1 mg (Mettler Toledo, ME204) for real-time measurement of the evaporation rate of water. The whole setup was allowed to stabilize for 30 min under 1 kW m⁻² and the time-dependent evaporation rate of water was recorded by an advanced electronic balance. All the evaporation rates were carefully recorded under multiple solar intensities. The surface temperature elevation of solar evaporators’ surfaces was recorded using EYSIGHT (34972 A) employing two temperature-sensing thermo-couples mounted on the photothermal surface and bottom surface, respectively, and an infrared thermal camera (FLIR E4 Pro, America). The salt rejection potential was determined by recording the ion concentration before and after desalination using ICP–OES (EP Optimal 8000). Generally, all the experimental procedures were carried out under ambient environmental conditions, for example, room temperature (25 °C) and humidity (42%).

CFD Simulations

Salt rejection through the open porous assembly of polyurethane wicks was simulated using CFD simulations through advanced COMSOL Multiphysics Software (5.5). Based on the actual dimensions of a single polyurethane wick, the momentum, energy, and salt transportation (convection) for a single wick was numerically computed to derive the temperature and velocity perturbations throughout the region via the 3D finite volume method (FVM).^[42] For this, the top interfacial surface possessed higher salinity as compared to the bottom bulk media followed by salinity gradient potential. Moreover, Ni et al.^[42] reported a detailed analysis of salt rejection through localized wicks and numerically computed the governing equations of the pressure-based segregated algorithm, which is an iteration procedure where logical manners are applied to resolve each equation.^[42]

For liquid, the energy equation can be given as3$\rho C_{\mathrm{p}}\left(u\frac{\partial T}{\partial x}+v\frac{\partial T}{\partial y}+w\frac{\partial T}{\partial z}\right)=k\left(\frac{{\partial }^{2}T}{\partial x^2}+\frac{{\partial }^{2}T}{\partial y^2}+\frac{{\partial }^{2}T}{\partial z^2}\right)$

By resolving the convection equation of salt concentration, the local salt mass fraction can be computed.4$\frac{\partial \left(\rho uC\right)}{\partial x}+\frac{\partial \left(\rho vC\right)}{\partial y}+\frac{\partial \left(\rho wC\right)}{\partial z}=\frac{\partial \left(\rho D\frac{\partial C}{\partial x}\right)}{\partial x}+\frac{\partial \left(\rho D\frac{\partial C}{\partial y}\right)}{\partial y}+\frac{\partial \left(\rho D\frac{\partial C}{\partial z}\right)}{\partial z}$

The variables that appeared in Equation (4) are specified in Table 1.

Table 1 The variables that appeared in Equation (4) are specified and it is worth noting that ρ presents the density of the liquid (seawater) which varies spatially

u	Velocity in x direction	μ	Dynamic viscosity
υ	Velocity in y direction	$C_p$	Specific heat transfer
w	Velocity in z direction	ρ	Liquid density (water plus dissolved salt)
P	Pressure	k	Thermal conductivity coefficient
T	Temperature	D	Mass diffusion coefficient
g	Gravity acceleration	β	Volumetric thermal expansion coefficient
C	Salt concentration

Acknowledgements

The authors thank the technical facilitation offered by the Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials and the Hubei Key Laboratory of Polymer Materials (Hubei University, Wuhan, P.R. China) under the supervision of Prof. Xianbao Wang for their support in experimental work. The authors are grateful for financial support from the National Key R&D Program of China (2019YFB2204500) and the Shenzhen Science and Technology Program (JCYJ20200109113606007).

Conflict of Interest

The authors declare no conflict of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

Y. Zhang, S. C. Tan, Nat. Sustainability 2022, 5, 554.

X. Li, T. Cooper, W. Xie, P.-C. Hsu, ACS Energy Lett. 2021, 6, 2645.

X. Li, W. Xie, J. Zhu, Adv. Sci. 2022, 9, 2104181.

Y. Zhang, T. Xiong, D. K. Nandakumar, S. C. Tan, Adv. Sci. 2020, 7, 1903478.

T. Gao, X. Wu, Y. Wang, G. Owens, H. Xu, Sol. RRL 2021, 5, 2100053.

M. S. Irshad, N. Arshad, X. Wang, Global Challenges 2021, 5, 2000055.

Y. Wang, X. Wu, P. Wu, J. Zhao, X. Yang, G. Owens, H. Xu, Sci. Bull. 2021, 66, 2479.

T. Gao, Y. Li, C. Chen, Z. Yang, Y. Kuang, C. Jia, J. Song, E. M. Hitz, B. Liu, H. Huang, J. Yu, B. Yang, L. Hu, Small Methods 2019, 3, 1800176.

W. Xu, X. Hu, S. Zhuang, Y. Wang, X. Li, L. Zhou, S. Zhu, J. Zhu, Adv. Energy Mater. 2018, 8, 1702884.

T. Ahmad Wani, P. Garg, S. Bera, S. Bhattacharya, S. Dutta, H. Kumar, A. Bera, J. Colloid Interface Sci. 2022, 612, 203.

X. Wu, Y. Wang, P. Wu, J. Zhao, Y. Lu, X. Yang, H. Xu, Adv. Funct. Mater. 2021, 31, 2102618.

X. Wu, Z. Wu, Y. Wang, T. Gao, Q. Li, H. Xu, Adv. Sci. 2021, 8, 2002501.

Y. Wang, X. Wu, T. Gao, Y. Lu, X. Yang, G. Y. Chen, G. Owens, H. Xu, Nano Energy 2021, 79, 105477.

H. D. Pham, L. Xianqiang, W. Li, S. Manzhos, A. K. K. Kyaw, P. Sonar, Energy Environ. Sci. 2019, 12, 1177.

M. Xu, W. Wang, Y. Liu, Y. Zhong, X. Xu, Y. Sun, J. Wang, W. Zhou, Z. Shao, Sol. RRL 2019, 3, 1900108.

D. Duan, X. Fang, K. Li, Talanta 2022, 240, 123112.

A. Aguadero, D. Pérez-Coll, J. A. Alonso, S. J. Skinner, J. Kilner, Chem. Mater. 2012, 24, 2655.

H. A. Tahini, X. Tan, W. Zhou, Z. Zhu, U. Schwingenschlögl, S. C. Smith, Energy Storage Mater. 2017, 9, 229.

M. S. Irshad, X. Wang, M. Abbasi, N. Arshad, Z. Chen, Z. Guo, L. Yu, J. Qian, J. You, T. Mei, ACS Sustainable Chem. Eng. 2021, 9, 3887.

X. Wang, Q. Liu, S. Wu, B. Xu, H. Xu, Adv. Mater. 2019, 31, 1807716.

F. Yu, Z. Chen, Z. Guo, M. S. Irshad, L. Yu, J. Qian, T. Mei, X. Wang, ACS Sustainable Chem. Eng. 2020, 8, 7139.

X. Zhou, F. Zhao, Y. Guo, B. Rosenberger, G. Yu, Sci. Adv. 2019, 5, eaaw5484.

X. Chen, P. Cheng, Z. Tang, X. Xu, H. Gao, G. Wang, Adv. Sci. 2021, 8, 2001274.

Z. Guo, W. Zhou, N. Arshad, Z. Zhang, D. Yan, M. S. Irshad, L. Yu, X. Wang, Carbon 2022, 186, 19.

R. Gulfam, P. Zhang, Z. Meng, Appl. Energy 2019, 238, 582.

T. Gao, Y. Wang, X. Wu, P. Wu, X. Yang, Q. Li, Z. Zhang, D. Zhang, G. Owens, H. Xu, Sci. Bull. 2022, 67, 1572.

A. Demharter, Cryogenics 1998, 38, 113.

M. S. Irshad, N. Arshad, X. Wang, H. R. Li, M. Q. Javed, Y. Xu, L. A. Alshahrani, T. Mei, J. Li, Sol. RRL 2021, 5, 2100427.

Q. Qi, Y. Wang, W. Wang, X. Ding, D. Yu, Sci. Total Environ. 2020, 698, 134136.

H. M. Wilson, S. R. AR, A. E. Parab, N. Jha, Desalination 2019, 456, 85.

Y. Xia, Q. Hou, H. Jubaer, Y. Li, Y. Kang, S. Yuan, H. Liu, M. W. Woo, L. Zhang, L. Gao, H. Wang, X. Zhang, Energy Environ. Sci. 2019, 12, 1840.

Q. Zhang, X. Xiao, G. Zhao, H. Yang, H. Cheng, L. Qu, W. Xu, X. Wang, J. Mater. Chem. A 2021, 9, 10945.

Y. Zhu, G. Tian, Y. Liu, H. Li, P. Zhang, L. Zhan, R. Gao, C. Huang, Adv. Sci. 2021, 8, 2101727.

L. Song, P. Mu, L. Geng, Q. Wang, J. Li, ACS Sustainable Chem. Eng. 2020, 8, 11845.

M. S. Irshad, X. Wang, A. Abbas, F. Yu, J. Li, J. Wang, T. Mei, J. Qian, S. Wu, M. Q. Javed, Carbon 2021, 176, 313.

Y. Shi, C. Zhang, R. Li, S. Zhuo, Y. Jin, L. Shi, S. Hong, J. Chang, C. Ong, P. Wang, Environ. Sci. Technol. 2018, 52, 11822.

Y. Lu, D. Fan, Z. Shen, H. Zhang, H. Xu, X. Yang, Nano Energy 2022, 95, 107016.

F. Yu, Z. Guo, Y. Xu, Z. Chen, M. S. Irshad, J. Qian, T. Mei, X. Wang, ACS Appl. Mater. Interfaces 2020, 12, 57155.

C. Gao, J. Zhu, Z. Bai, Z. Lin, J. Guo, ACS Appl. Mater. Interfaces 2021, 13, 7200.

Z. Lei, X. Sun, S. Zhu, K. Dong, X. Liu, L. Wang, X. Zhang, L. Qu, X. Zhang, Nano-Micro Lett. 2022, 14, 1.

Q. Zhang, H. Yang, X. Xiao, H. Wang, L. Yan, Z. Shi, Y. Chen, W. Xu, X. Wang, J. Mater. Chem. A 2019, 7, 14620.

G. Ni, S. H. Zandavi, S. M. Javid, S. V. Boriskina, T. A. Cooper, G. Chen, Energy Environ. Sci. 2018, 11, 1510.

M. S. Irshad, X. Wang, N. Arshad, M. Q. Javed, T. Shamim, Z. Guo, H. R. Li, J. Wang, T. Mei, Environ. Sci. Nano 2022, 9, 1685.