Doping Shortens the Metal/Metal Distance and Promotes OH Coverage in Non-Noble Acidic Oxygen Evolution Reaction Catalysts

Abstract

Acidic water electrolysis enables the production of hydrogen for use as a chemical and as a fuel. The acidic environment hinders water electrolysis on non-noble catalysts, a result of the sluggish kinetics associated with the adsorbate evolution mechanism, reliant as it is on four concerted proton-electron transfer steps. Enabling a faster mechanism with non-noble catalysts will help to further advance acidic water electrolysis. Here, we report evidence that doping Ba cations into a Co3O4 framework to form Co3–x Ba x O4 promotes the oxide path mechanism and simultaneously improves activity in acidic electrolytes. Co3–x Ba x O4 catalysts reported herein exhibit an overpotential of 278 mV at 10 mA/cm2 in 0.5 M H2SO4 electrolyte and are stable over 110 h of continuous water oxidation operation. We find that the incorporation of Ba cations shortens the Co–Co distance and promotes OH adsorption, findings we link to improved water oxidation in acidic electrolyte.

Boosting CeO2/Co3O4 Heterojunctions Acidic Oxygen Evolution via Promoting OH Coverage

“…These results demonstrate that C@CeO 2 /Co 3 O 4 induces faster rates of electron and ion transport, both of which favor the water molecule dissociation and intermediate transport (*H 2 O, *OH, etc.) at the interface . In summary, it can be deduced that C@CeO 2 /Co 3 O 4 accelerates the reaction kinetic process compared to Co 3 O 4 , C/Co 3 O 4 , and CeO 2 /Co 3 O 4 .…”

Direct Dioxygen Radical Coupling Driven by Octahedral Ruthenium–Oxygen–Cobalt Collaborative Coordination for Acidic Oxygen Evolution Reaction

“…, 1.76 and 1.86 V vs RHE) for the Co 3 O 4 . This is not surprising since the 18 O isotope-labeled DEMS experiment has previously demonstrated that Co 3 O 4 spinel can realize the diatomic O–O radical coupling in acid …”

“…This indicates that the OER over the RuCoO x could possibly proceed with an unusual DOM reaction pathway driven by the heteroatomic Ru oct –O–Co oct units. The DOM involves the adsorption of the *OH intermediate, the subsequent dehydrogenation, and the final dioxygen radical coupling process (Figure c), which has been widely studied in theoretical and experimental aspects. − We then further calculated the bond lengths and the bond angles of the Ru oct –O–Co oct units and found that they are highly symmetrical (Figure e) along with shortened atomic distances (Figure g). Both are beneficial to conducting the final O–O radical coupling with a low thermodynamic energy barrier. ,, Indeed, our simulation shows that the required free energy of the dioxygen radical coupling to form O 2 is as low as 1.17 eV (Figure S19a, Table S4), which further suggests that the OER over the RuCoO x might proceed with the DOM reaction pathway.…”

“…This is not surprising since the 18 O isotope-labeled DEMS experiment has previously demonstrated that Co 3 O 4 spinel can realize the diatomic O−O radical coupling in acid. 31 The dissolution of Co species can further be indirectly reflected by the change in the Co III /Co II ratio (corresponding to integral area of A 1g /F 2g peaks) based on the in situ Raman analysis. The Co III /Co II ratio of the RuCoO x only slightly elevates upon the OER potentials (Figure 5f), suggesting the highly structural integrity of the RuCoO x under positive bias, well in with the Co 2p XPS and CV analysis (Figure 5b,d).…”

“…, Co oct ) sites, for instance, by atomic substitution, therefore provides an effective way to regulate the coordination environment of Co 3 O 4 and further boost the OER performance. In addition, previous studied have demonstrated a diatomic oxygen mechanism (DOM) over Co 3 O 4 for OER. − The DOM proceeds with direct dioxygen radicals coupling to release O 2 , which can effectively circumvent the formation of the *OOH intermediate and thus break the *OH and *OOH scaling relationship limitation of the traditional adsorbate evolution mechanism (AEM). , In this regard, the precise substitution of octahedral Co with other atoms might also enable the DOM pathway and significantly enhance the acidic OER performance, though it has not been realized yet.…”