Generation of H₂, from water electrolysis using renewable sources, is important to reduce CO₂ emissions. However, platinum group metal (PGM) electrocatalysts are commonly used to facilitate the hydrogen evolution reaction (HER) both in acid and alkaline electrolyte. One of the challenges for HER is to reduce the loading of PGMs, while still maintaining high HER activity. Transition metal carbides (TMCs) and nitrides (TMNs) have been reported to sometimes exhibit catalytic activities of PGMs making them potential materials that can be used to support low-loadings of PGMs for HER. Previous studies have shown promise for TMCs as supports for monolayer (ML) amounts of Pt for HER. Though TMNs have not been extensively explored for this application, they are thought to have a cleaner surface after synthesis than TMCs leading to a more direct interaction with the supported Pt. In addition, it is well established that hydrogen binding energy (HBE) is a key descriptor for HER activity and has been demonstrated for PGMs on TMCs. In almost all cases, however, the HBE values are obtained from density functional theory (DFT) calculations. In this study, temperature programmed desorption (TPD) was used to experimentally determine the HBE values of metal MLs supported on molybdenum nitride (Mo₂N) thin films. Electrochemical measurements were performed on the same surfaces, in both acid and alkaline electrolyte, to determine HER activities and correlate them with TPD-determined HBE values. Combined DFT and kinetic Monte Carlo (kMC) simulations were used to validate the trend observed with TPD and the electrochemical HER activity. Depositing one monolayer of Pt on Mo₂N led to similar HBE values seen for bulk Pt as determined by both TPD and DFT. Electrochemical measurements showed that monolayer Pt on Mo₂N had similar HER activity to that of bulk Pt in both acid and alkaline electrolyte. Similar studies were also performed for monolayer Pd on Mo₂N to confirm the correlation. This work also demonstrates that Mo₂N is a promising support to reduce precious metal loading in HER catalysts.

Wenjie Liao

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