Research progress in anode transition metal-based catalysts for direct methanol fuel cell

The development of alternative energy resources is of great significance to alleviate the global energy issue. The direct methanol fuel cell (DMFC) is gradually becoming one of the most promising portable energy technologies due to the merits of low operating temperature, high energy density, and low pollutant emission. Currently, its commercialization process mainly depends on the kinetics of the anodic methanol oxidation reaction (MOR). Noble metals have been widely studied as the most commonly used anode catalysts. However, high prices and limited reserves have severely hindered their further development. In addition, the active surface of Pt is susceptible to the poison of CO_ads intermediate products, leading to the rapid loss of the catalytic activity due to blocked Pt sites. Considering the above problems, the design and development of low Pt or non-Pt nanocatalysts with an excellent antipoisoning ability have become very important. Transition metals have been widely used as promising substitutes for noble metal catalysts because of their abundant reserves, low price, and high catalytic activity. Among the transition metals studied, Ni, Cu, and Co have attracted sustained attention because of their high corrosion resistance. Owing to the ligand effect and synergistic effect, the addition of transition metals can effectively weaken the adsorption of CO_ads intermediates on Pt sites. At the same time, non-noble transition metals are easy to form MOOH active species, which promote the oxidation of CO_ads intermediates. Besides, methanol electrooxidation performance is closely related to the shape, structure, and composition of transition metals. From the principle of DMFC anode electrocatalysis, this review summarized the research progress of transition metal-based catalysts (transition metal-noble metal catalysts, transition metal catalysts, and self-supporting catalysts) in MOR. More importantly, the effects of the nanocatalyst composition, porous structure, high-index surface, crystal defects, and vertex enhancement on its electrochemical properties were emphasized. Finally, opportunities and challenges faced by transition metal-based electrocatalysts in DMFC were discussed.