Oxygen‐Deficient Cobalt‐Based Oxides for Electrocatalytic Water Splitting

Abstract

An apparent increased interest has been recently devoted towards the previously untrodden path for anionic point defect engineering of electrocatalytic surfaces. The role of vacancy engineering in improving photo‐ and electrocatalytic activities of transition metal oxides (TMOs) has been widely reported. In particular, oxygen vacancy modulation on electrocatalysts of cobalt‐based TMOs has seen a fresh spike of research work due to the substantial improvements they have shown towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Oxygen vacancy engineering is an effective scheme to quintessentially tune the electronic structure and charge transport, generate secondary active surface phases, and modify the surface adsorption/desorption behavior of reaction intermediates during water splitting. Based on contemporary efforts for inducing oxygen vacancies in a variety of cobalt oxide types, this work addresses facile and environmentally benign synthesis strategies, characterization techniques, and detailed insight into the intrinsic mechanistic modulation of electrocatalysts. It is our foresight that appropriate utilization of the principles discussed herein will aid researchers in rationally designing novel materials that can outperform noble metal‐based electrocatalysts. Ultimately, future electrocatalysis implementation for selective seawater splitting is believed to depend on regulating the surface chemistry of active and stable TMOs.

Dynamic Surface Chemistry of Catalysts in Oxygen Evolution Reaction

“…[ 55 ] Photoluminescence spectroscopy (PL) is also a useful characterization technique for studying electronic changes of materials and determining the degree of oxygen deficiency. [ 56 ] The presence of oxygen vacancies generates new electronic states near the Fermi level and generally modulates the bulk electronics of a material. Peak position and intensity of the PL spectra can easily identify changes that occur upon such electronic modulations from oxygen vacancies.…”

Activating the lattice oxygen oxidation mechanism in amorphous molybdenum cobalt oxide nanosheets for water oxidation

“…Transition metal oxides (TMOs) have been widely explored as promising electrocatalysts for OER in alkaline medium (4OH − → O 2 + 2H 2 O + 4e − ). 22–25 Within a LOM mechanism, to optimize the OER performance of a catalyst, the oxygen p band needs to be shifted close to the Fermi level to trigger the redox activity of the lattice oxygen. This requires strong metal d- and oxygen p-band overlap.…”

Boosting Oxygen Evolution Reaction on Metallocene‐based Transition Metal Sulfides Integrated with N‐doped Carbon Nanostructures

“…Water electrolysis based on alkaline solution is considered as the promising, low‐cost, and sustainable way to produce hydrogen fuel compared to water electrolysis under acidic condition since the numerous non‐noble and earth‐abundant electrocatalysts are highly active and relatively stable against corrosion in alkaline solution [32] . In contrast, precious metals and their oxides only showed outstanding electrocatalytic activity in acidic electrolyte medium, and also their instability under long‐term operation along with the high cost limits the commercialization.…”

“…In contrast, precious metals and their oxides only showed outstanding electrocatalytic activity in acidic electrolyte medium, and also their instability under long‐term operation along with the high cost limits the commercialization. However, due to the sluggish kinetics of OER associated with the multiple adsorbed oxygen intermediates such as *OOH, *O, and *OH, additional voltage is always required for the non‐noble metal‐based electrocatalysts to split the water molecules compared to the thermodynamic potential (i. e., 1.23 V RHE ) for the water oxidation [32] . Thus, we here developed the non‐noble and earth‐abundant electrocatalysts based on transition metal sulfides derived from metallocene for the outstanding OER in alkaline conditions.…”