Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Photoelectrochemical (PEC) water splitting is considered as a promising technology for producing clean energy such as hydrogen. The urgent challenge in this field is how to prepare highly efficient electrode materials. The introduction of oxygen vacancies (OVs) into catalytic materials has been confirmed to be an effective strategy toward enhancing the performance of PEC water splitting by both theoretical calculations and experiment results. Herein, the existing strategies for introducing OVs into nanomaterials are discussed in this minireview. In addition, the effect of OVs on PEC water splitting to improve the light absorption efficiency, charges transfer efficiency, and charge injection efficiency was summarized. Finally, we propose several challenges that need to be addressed in the field of PEC water splitting in the future. This minireview could offer some important contributions to the future synthesis of nanomaterials with rich OVs for PEC application. 

Oxygen Vacancy-Based Metal Oxides Photoanodes in Photoelectrochemical Water Splitting

Unveiling the promotion of accelerated water dissociation kinetics on the hydrogen evolution catalysis of NiMoO4 nanorods

La-doped NiFe-LDH coupled with hierarchical vertically aligned MXene frameworks for efficient overall water splitting

Perovskite transition metal oxides with ABO3 structure are considered as potential alternative non-precious metal electrocatalysts for designing highly active and durable electrocatalysis for the oxygen evolution reaction (OER). Herein, we successfully enable LaFeO3 coated on nickel foam (denoted LFO@NF) perovskite with impressive OER activity by systematically tailoring the Fe cation sites and the introduction of oxygen vacancies. The cationic site involves dual cation modulation with Cr and Mo, which creates lattice distortions inducing strong electronic interaction, while the anionic site entails reduction via a hydrogen-treatment process, creating oxygen vacancy sites to improve the electronic conductivity of the perovskite oxide. As a result, the optimized LFO-based catalyst, specifically hydrogenated LaFe0.75Cr0.15Mo0.10O3-coated on the nickel foam (denoted H-LFCMO@NF), requires the lowest overpotential of 263 mV at 10 mA cm−2, and has superior kinetics and excellent stability, which are superior to its counterparts. Theoretical analysis also confirmed that the tailoring of the LFO@NF perovskite leads to an increase in the exposure of active sites, optimization of the adsorption energy of reaction intermediates and enhanced electronic conductivity. This work may provide a promising concept to enhance the performance of LFO-based perovskite electrocatalysts for alkaline OER and beyond.

A Paul Blessington Selvadurai

Papers

Tailoring the cationic and anionic sites of LaFeO3-based perovskite generates multiple vacancies for efficient water oxidation