Lithiation-induced modification of crystallinity of C-doped FexOy for highly efficient hydrogen evolution reaction

초록

With the rapid increase in energy demand, the use of fossil fuels has been on the rise, resulting in the emission of harmful gases such as carbon dioxide, nitrogen oxides (NOx), and sulfur oxides (SOx), which cause various environmental problems. Hydrogen is classified into three types, namely gray hydrogen, blue hydrogen, and green hydrogen, depending on the manufacturing method. Among them, water electrolysis belonging to green hydrogen has considered as an eco-friendly alternative energy due to its low emission of pollutants. However, expensive noble metal catalysts are mainly used to minimize the overpotential of water electrolysis. Thus, many researchers are conducting numerous studies to replace expensive noble metal catalysts with cheaper transition metal catalysts for commercialization. In this study, we used a stainless steel substrate containing various inexpensive transition metal elements such as Fe, Ni, Cr, and Mo. We hydrothermally treated the stainless steel with an oxalic acid solution to create iron oxalate, and then annealed in an Ar atmosphere to produce C-doped iron oxide with doped-carbon derived from the oxalate decomposition process. Lithiation-induced electrochemical activation was employed in a lithium-ion battery to achieve nanostructuring and amorphization. As the number of cycles increases, the degree of amorphization increased, and the amorphous-crystalline heterostructure with optimized cycle number showed the highest HER activity. In addition, we presented the possibility of recovering the excessively amorphous structures caused by long-term battery cycling through heat treatment.