Tuning electrocatalytic water oxidation by MnOx through the incorporation of abundant metal cations

Abstract

Layered manganese oxides which were deposited on carbon fibre paper (MnO_x/CFP) via a redox-deposition process show promising activities and stabilities for the OER over a very wide pH range. In the study presented here, the influence of the incorporation of metal cations (Mⁿ⁺, M = Ca, Co, Ni, Fe) into MnO_x layers on the OER performance at different pH values (2.5/7.0/14.0) is explored. Spectroscopic analyses of M_yMnO_x/CFP reveal that doping with other metal cations does not alter the basic birnessite-type MnO_x structure. However, the average manganese oxidation state can be tuned and is found to depend on the incorporated metal cations. Furthermore, a clear dependence of the catalytic activity and stability on the incorporated metal ion is observed and especially Ni- and Co-doping lead to a significant performance boost under alkaline (Ni and Co) and neutral conditions (Co). A comparison to other state-of-the-art metal oxide catalysts (also deposited on CFP for comparison) shows that the metal-doped M_yMnO_x/CFP anodes are able to compete with the most active materials known so far.