Strategies for Modulating the Catalytic Activity and Selectivity of Manganese Antimonates for the Oxygen Reduction Reaction

Strategies for improving the performance of nonprecious
metal catalysts
for the oxygen reduction reaction (ORR) can facilitate the cost-effective
deployment of fuel cell devices. Electrocatalyst performance is typically
improved via two approaches: increasing the number of active sites
and increasing the intrinsic activity of the active site. Herein,
we utilize these two methods of improving performance for MnSb2O6, which we have recently shown to be a promising
ORR catalyst due to improvements in per-metal-site activity in the
antimonate framework. First, electrode engineering is used to investigate
the role of mass and conductive support loading in the observed ORR
performance and selectivity. The apparent 2-electron selectivity is
found to decrease with increases in mass and/or conductive support
loading, indicating that rotating ring disk electrode studies do not
necessarily measure the intrinsic selectivity of the catalyst. Second,
theoretical calculations are used to identify Cr, Fe, and Ni as promising
first-row transition metals for improving the intrinsic activity of
MnSb2O6. Experimentally, the addition of Cr
results in 3-fold and 2-fold increases in the mass and specific activities
at 0.7 V vs the reversible hydrogen electrode, respectively. This
enhancement is attributed to the modulation of the active site structure
and Mn oxidation state with the addition of Cr. Through these studies,
we gain insight into the intrinsic and extrinsic factors that govern
ORR performance.

提升氧还原反应（oxygen reduction reaction, ORR）中非贵金属催化剂性能的策略，可助力燃料电池设备实现低成本高效部署。电催化剂的性能优化通常通过两种途径实现：一是增加活性位点的总数，二是提升活性位点的本征催化活性。本文针对MnSb2O6应用上述两种性能优化策略展开研究；我们近期的研究已证实，该锑酸盐骨架催化剂凭借单位金属位点活性的提升，是一款极具应用前景的ORR催化剂。首先，本研究采用电极工程方法，探究催化剂质量负载量与导电载体负载量对观测到的ORR性能及选择性的影响。研究发现，表观双电子选择性随质量负载量或导电载体负载量的增加而降低，这表明旋转环盘电极测试未必能直接测得催化剂的本征选择性。其次，通过理论计算筛选出Cr、Fe、Ni三种极具潜力的第一过渡系金属，用于提升MnSb2O6的本征催化活性。实验结果表明，掺入Cr后，在相对于可逆氢电极0.7 V的电位下，催化剂的质量活性与比活性分别提升了3倍与2倍。该性能增强可归因于Cr掺入后活性位点结构与Mn氧化态的调控。通过上述研究，我们深入阐明了调控氧还原反应催化性能的本征与外在影响因素。