Metal phosphides as efficient catalysts for methanol oxidation reaction.

The methanol oxidation reaction (MOR) is a key anodic process in sustainable energy conversion and the synthesis of value-added chemicals. While noble metals such as Pt and Pd exhibit high catalytic activity, their practical use is limited by high cost, poor stability in alkaline media, and the generation of pollutant gaseous byproducts. In contrast, transition metal phosphides (TMPs) have emerged as promising alternatives due to their tunable composition, strong resistance to catalyst poisoning, chemical robustness under alkaline conditions, and high selectivity for liquid formate, a valuable chemical with a current market price exceeding that of methanol. Although TMPs were initially studied as promoters for noble metal catalysts, recent research has shifted toward evaluating their performance as standalone catalysts for MOR. These systems typically require higher operating potentials (above 1.4 V vs. RHE) compared to noble-metal-based catalysts (0.8-1.1 V vs. RHE) but offer the advantage of avoiding CO and CO2 emissions while maintaining high selectivity toward formate. A central challenge in comparing TMPs to noble metal systems stems from inconsistent data normalization practices in the literature: activity is often reported per mass of noble metal, rather than per total catalyst mass. When normalized to the total mass, TMP-based systems may exhibit comparable or even superior mass activity, suggesting their viability despite the higher required potential. Research to date has focused largely on Ni- and Co-based TMPs, while Fe- and Mo-based variants, although efficient in combination with noble metals, remain underexplored as independent catalytic materials and warrant further investigation.