Nickel-based materials have been extensively studied as methanol oxidation reaction (MOR) catalysts. The formation of NiOH and its reduction to Ni(OH)2 is generally considered to be an important step in the oxidation of methanol. However, in this indirect pathway, the efficiency of proton-coupled electron transfer (PCET) is fundamentally limited by the rate of Ni(OH)2 to NiOOH back-and-forth transitions. Based on this,Wang Fuxian, researcher (corresponding author), Institute of Testing and Analysis, Guangdong Academy of Sciences, et alA direct MO path on MoO3 Ni(OH)2 is reported without the formation of NiOH media. moO3 ni(oh)2 in 152 v vs.It exhibits a benchmark electrocatalytic Mor current density of 1000 mA cm-2 at RHE with a Faraday efficiency of close to 100%, which is better than all current MOR electrocatalysts.
In order to elucidate the influence of the unique structure of MoO3 Ni(OH)2 on the mechanism and properties of the MOR, the energy of the MOOR process is calculated by density functional theory (DFT) method. The adsorption energy of methanol at the Ni site is greater than that at the Mo site, so the unsaturated coordination Ni site is more likely to be the adsorption and active site of Mor on MoO3 Ni(OH)2. However, the MO site plays an important role in the extraction of H· from methanol, and the Bader charge analysis and Mo-H bond length indicate that the MO site has a stronger ability to capture H·.
For Ni(OH)2, due to the weak adsorption of H·, the desorption energy of methanol intermediates is high, and the PCET process of methanol is relatively difficult, resulting in a large energy barrier in the CH2O* CHO*+H* process (152 ev）。Due to the low energy barrier required for the conversion of Ni(OH)2 to NioOH, Ni sites tend to convert to NiOH to drive the MOR process. In contrast, for MoO3 Ni(OH)2, H· has strong adsorption at the Mo site, and the energy barrier of CH2O* CHO* +H* is only -003 EV, showing the synergistic catalytic effect of NI-MO. The highest barrier for moo3 ni(oh)2 is only 023 V, which is much lower than the energy barrier required to convert Ni(OH)2 to NiOOH. Therefore, the Ni site in MoO3 Ni(OH)2 is more inclined to directly catalyze methanol oxidation rather than auto-oxidation to NiOH generation.
direct electrocatalytic methanol oxidation on moo3/ni(oh)2: exploiting synergetic effect of adjacent mo and ni. j. am. chem. soc.,, doi: 10.1021/jacs.3c09399.
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