Ni-Fe hydroxide derived from Ni-Fe oxalate for highly efficient oxygen evolution reaction

초록

Fossil fuels have limited reserves and combustion of them produces carbon dioxide, nitrogen oxides (NOx), and sulfur oxides (SOx) which is a major cause of environmental problems. To replace these fossil fuels, various alternative energies are being developed. Among them, hydrogen has attracted attention as next-generation alternative energy due to low emission of pollutants. Methods for producing hydrogen include fossil fuel reforming, biological methods, and water electrolysis, among which water electrolysis causes relatively little environmental pollution. Although many studies are being conducted to increase the efficiency of water electrolysis, most of the catalysts with high-water-electrolysis performance are noble metal catalysts (Pt, Ru, Ir), which are expensive, thus hindering commercialization. To overcome these limitations, many studies on alkaline water electrolysis systems that can use relatively inexpensive and abundantly reserved transition metal-based catalysts are being conducted. However, the transition metal catalyst still has a higher overpotential and lower stability than the noble metal catalyst. Iron-based bimetallic catalysts are known to show superior performance than single catalysts because iron acts as a co-catalyst for generating oxygen when composed of a binary catalyst with nickel or cobalt. Therefore, since Ni-Fe binary catalysts exhibit excellent activity for oxygen evolution reaction, studies on oxygen evolution reaction performance in various structures such as oxides, chalcogenides, and (oxy)hydroxides are being conducted. In this study, a large-area nickel foam was immersed in a solution of iron(III) chloride and oxalic acid without special equipment at room temperature to form a nanostructured Ni-Fe oxalate in various ratios on the surface. It was confirmed that the electrochemically active surface area and electrical conductivity change according to the Ni/Fe ratios, and the oxygen evolution performance changes accordingly.