One-pot hydrothermal synthesis of Co–Ni hexacyanoferrate nanocuboids on Ni-foam as efficient catalysts for oxygen evolution and urea oxidation reactions

Abstract

Recently, considerable research has been conducted on Prussian blue analogues (PBAs), a type of metal-organic framework (MOF) material, as novel electrocatalysts for oxygen evolution reactions (OERs) and urea oxidation reactions (UORs). In the present work, considering Co–Ni hexacyanoferrate (Co_xNi_1−xHCF) as a PBA, Co_xNi_1−xHCF nanocuboids with different Co and Ni compositions were synthesized on Ni foam (NF) by hydrothermal synthesis. Further, their application toward OER and UOR catalytic activity was studied. The synthesized Co_xNi_1−xHCF:NF composites with high catalytic activity and conductivity exhibited superior catalytic performance for the OERs and UORs. The Co_xNi_1−xHCF:NF composite electrodes exhibited a lower overpotential (η) of 334 mV with a lower Tafel slope of 72 mV dec⁻¹ for the OER catalytic activity and a lower potential of 1.38 V with a lower Tafel slope of 50 mV dec⁻¹ for the UOR catalytic activity. It was observed that low charge transfer resistance, high electrochemically active surface area, and availability of Co³⁺ ions are major factors contributing to the OER activity. The presence of oxidative Ni²⁺ species contributed significantly to the UOR activity. Overall, the present study elucidates the binder-free Co_xNi_1−xHCF:NF electrodes as stable and high-performance OER and UOR catalysts and provides pathways for designing advanced PBA catalysts.