Synthesis and Electrocatalytical Application of Hybrid Pd/Metal Oxides/MWCNTs

Received Jan 26, 2018; Accepted May 8, 2018

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1. Introduction

Growing environmental pollution and the fact that crude oil resources are going to be exhausted stimulate an intensive development of work on replacing petroleum fuels by biofuels and by application of fuel cells for production of electricity. The application of biofuels results in reducing the emission of CO₂ and other pollutants. The content of CO₂ emitted in conversion of biofuels is equivalent to the respective content absorbed from the atmosphere by green plants in a process of biosynthesis; thus the application of biofuels as energy sources leads to overall CO₂ zero emission, what is very important for decreasing of the effects of global warming. Fuel cells are the most efficient electrical energy producing devices, operating using fuels and oxygen as reactants. Fuel cells directly transform chemical energy to electric energy with high efficiency. The most common fuels are hydrogen in proton exchange membrane fuel cells (PEMFCs), methanol in direct methanol fuel cells (DMFC), and formic acid in direct formic acid fuel cells (DFAFC). All these fuels can be produced from biomass. Fuel cells operating on liquid fuels for small and medium scale applications have prospects of commercialisation, and low temperature direct formic acid fuel cells (DFAFC) appear among the most promising in this respect [1]. DFAFC has a number of advantages over direct methanol fuel cells [1]: (i) it has higher power density and higher energy efficiency, (ii) crossover flux of formic acid through Nafion® membrane is several times smaller than that of methanol [2], and (iii) formic acid is less toxic than methanol and does not have the risk of producing hazardous by-products during oxidation (e.g., formaldehyde). A number of reviews on DFAFC [1, 3–8] have been published.

The oxidation of formic acid in DFAFC proceeds according to the following scheme:

 

Anode: HCOOH → CO₂ + 2H⁺ + $\mathrm{2}{\mathrm{e}}^{\text{-}}$

 

Cathode: 1/2O₂ + 2H⁺ + $\mathrm{2}{\mathrm{e}}^{\text{-}}$ → H₂O

 

Overall reaction: HCOOH + 1/2O₂ → CO₂ + H₂O

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