Bifunctional Oxygen Electrocatalysis on Manganese Oxide

Abstract

Limited supply of precious metals impedes the scale up of electrolyzer production. To enable 100s of GWs of PEM electrolyzer capacity by 2030, iridium supply must grow by more than 10x.[1] Alternatively, catalysts made of cheaper, more abundant manganese could relieve these constraints, if engineered to have comparable activity and stability. The unique bifunctional OER/ORR activity of Mn oxide could also enable electrolyzers that both produce and consume fuel with a single catalyst. Yet rational design of Mn oxide catalysts requires a better understanding of the structural and chemical motifs that lead to high bifunctional performance.In this talk, we will discuss our investigation of the bifunctional OER & ORR activity of Mn oxide and its unusual pH dependence. Our model system, 𝛼-KxMnO2, is among the best reported Mn oxide catalysts for both the OER and the ORR, with ORR activity matching that of Pt.[2] While the OER activity of Mn oxide has been shown to increase at higher pH,[3] we will show that its ORR activity improves as well. We will discuss our attempts to understand this phenomenon with operando scanning transmission x-ray microscopy (STXM), which enables spectroscopic investigation of single catalyst particles during reaction with spatial resolution down to 25 nm. Complementary surface DFT calculations provide further evidence for identification of the active crystal facets and insights into the pH-dependency of the OER & ORR mechanisms. We will discuss the implications of this work on the design of bidirectional electrolyzers with low-cost, non-precious metal catalysts.[1] IRENA. Green Hydrogen Cost Reduction. 2020 [2] Meng, Y. et al. J. Am. Chem. Soc. 2014, 136 (32), 11452–11464.[3] Takashima, T. et al. J. Am. Chem. Soc. 2012, 134 (3), 1519–1527.