Transition Metal Carbides Electrocatalysts for Water Splitting

Abstract

Electrochemically splitting water into its two elemental components, hydrogen and oxygen, is being heavily investigated as a path toward renewable energy. Hydrogen has been viewed as an energy carrier which could store wind, solar, and other forms of renewable energy for later use. In order to develop the hydrogen economy, new stable, and economical water splitting catalysts need to be developed. Transition metal carbides (TMC) are robust materials consisting of only metal and carbon atoms. These compounds are electrically conducting, and resistant to degradation in conditions typical of electrochemical water splitting reactions. TMCs have been found to have an electronic structure that is similar to Pt and are being investigated as cost‐effective, stable materials for both hydrogen and oxygen reactions. These TMC catalysts have been modified using several approaches including forming nanoparticles to increase surface area, adding conducting carbon and doped carbon support materials, doping the metal carbide to alter the electronic structure, and creating heterointerfaces with other metals and compounds. Fundamental studies on the nitrogen (N‐doped) carbon composites have shown a significant synergistic effect by modifying the electronic structure and thus the hydrogen binding energy. The nitrogen sites also provide a unique and beneficial binding site for H atoms during the electrochemical process. The most challenging but promising area of study focuses on the combination of TMC compounds with another catalyst material to create optimized interfaces. These heterointerface materials are difficult to probe experimentally and further optimize but with advances in density‐functional theory (DFT) calculations, several predictive models have been established. Through these modifications, several catalyst systems have shown catalytic activity and stability that rivals precious metal catalysts at greatly reduced cost. In addition, some of the synthetic methods could be easily scaled for industrial applications. The future of TMC catalysts is extremely promising and with improvements in scalable synthesis methods, activity, and stability, these carbide catalysts will likely be utilized in commercial electrolysis applications.

Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

“…Traditionally, TiO 2 is perhaps one of the most classic photocatalysts for water splitting, [259] whereas Pt is one of the most active electrocatalysts among different transition metals (M) for water splitting reaction, the latter is well known from the volcano plot of the exchange current density versus the MH bond energy. [257,260,261] The understanding of the surface sites for the activation is thus very important. In an early in situ liquid cell TEM study of photocatalytically active TiO 2 and TiO 2 /Pt catalysts, the self-hydrogenated shell on the TiO 2 is shown to promote photocatalytic H 2 evolution.…”

Electrosynthesis of ruthenium nanocluster incorporated nickel diselenide for efficient overall water splitting

“…18,19 Currently, transition metal compounds including chalcogenides, oxides, hydroxides, carbides, phosphides, etc., are studied as potential candidates for HER and OER activity towards water splitting. [20][21][22][23][24][25][26] Recently, transition metal selenides have gained much more attention because of their d-orbital conguration and better conductivity. [27][28][29][30] However, their electrochemical activity is still far from that of the benchmark catalysts because of their high adsorption energy, low number of electrochemically active sites, etc.…”