Stabilization of a Mn−Co Oxide During Oxygen Evolution in Alkaline Media

Abstract

Improving the stability of electrocatalysts for the oxygen evolution reaction (OER) through materials design has received less attention than improving their catalytic activity. We explored the effects of Mn addition to a cobalt oxide for stabilizing the catalyst by comparing single phase CoO x and (Co 0.7 Mn 0.3 )O x films electrodeposited in alkaline solution. The obtained disordered films were classified as layered oxides using X-ray absorption spectroscopy (XAS). The CoO x films showed a constant decrease in the catalytic activity during cycling, confirmed by oxygen detection, while that of (Co 0.7 Mn 0.3 )O x remained constant within error as measured by electrochemical metrics. These trends were rationalized based on XAS analysis of the metal oxidation states, which were Co 2.7 + and Mn 3.7 + in the bulk and similar near the surface of (Co 0.7 Mn 0.3 )O x , before and after cycling. Thus, Mn in (Co 0.7 Mn 0.3 )O x successfully stabilized the bulk catalyst material and its surface activity during OER cycling. The development of stabilization approaches is essential to extend the durability of OER catalysts.

Effect of Different Metal Ions between Nanolayers of Manganese Oxide for Water Oxidation Reaction under Acidic Conditions

“…Comparing the reduction and oxidation peaks for Mn(II)/(IV) and (or) (III)/(IV) of this sample and the calcined sample at 60 °C, significantly bigger peaks were observed for the calcined sample at 600 °C (Figure S15j). The stabilization of CoO x by adding Mn during WOR was reported under alkaline conditions …”

Upgrading the Detection of Electrocatalyst Degradation During the Oxygen Evolution Reaction

“…by optimizing the composition. [47]  The elucidation of degradation has higher demands on experimental design as compared to activity (benchmarking) studies simply due to the needed long duration, during which important parameters, such as temperature and electrolyte concentration, need to be held constant. Optimizing the experimental design is particularly important for another positive recent direction of the field, namely the investigations of "industry-relevant" conditions of high currents, high electrolyte concentration and temperature above room temperature.…”

What X-ray absorption spectroscopy can tell us about the active state of earth-abundant electrocatalysts for the oxygen evolution reaction

“…[72][73][74] The analysis is only valid if the observed oxidation states are a combination of the reference states and no new electronic states emerge. The accuracy of the calibration plot is rarely discussed, yet we have shown calibration of the Mn oxidation state of manganese oxides at the Mn-K edge with an accuracy to about ±0.16 oxidation states 44 (rms error) using the area under the edge. The accuracy of the oxidation state calibration deserves a detailed discussion to be published elsewhere.…”

“…23,[40][41][42] Unfortunately, the electrochemical parameters are often ambiguous, especially when the conclusions rely 5/18 on a single mechanistic parameter such as the Tafel slope, since they may be influenced by concomitant processes, e.g., redox transformation of a electrocatalyst component or competing Faradaic reactions, as well as by additional factors including electrical conductivity, blocking of the electrode surface due to gas bubble formation, local pH changes, among others. 43,44 Therefore, complementary spectroscopic investigations as well as reaction product analysis are needed to corroborate the mechanistic insights gained by electrochemical methods. The assignment of physicochemical processes to the observed features in the CV is often unclear.…”