The Hydrogen Evolution Reaction in Alkaline Solution: From Theory, Single Crystal Models, to Practical Electrocatalysts

Abstract

The hydrogen evolution reaction (HER) is a fundamental process in electrocatalysis and plays an important role in energy conversion for the development of hydrogen-based energy sources. However, the considerably slow rate of the HER in alkaline conditions has hindered advances in water splitting techniques for high-purity hydrogen production. Differing from well documented acidic HER, the mechanistic aspects of alkaline HER are yet to be settled. A critical appraisal of alkaline HER electrocatalysis is presented, with a special emphasis on the connection between fundamental surface electrochemistry on single-crystal models and the derived molecular design principle for real-world electrocatalysts. By presenting some typical examples across theoretical calculations, surface characterization, and electrochemical experiments, we try to address some key ongoing debates to deliver a better understanding of alkaline HER at the atomic level.

Heteroatom‐doped MoSe2 Nanosheets with Enhanced Hydrogen Evolution Kinetics for Alkaline Water Splitting

“…Also, Ni‐doped MoSe 2 catalysts show decreased Tafel slopes (67–76 mV dec −1 ) compared with that of MoSe 2 (99 mV dec −1 ), indicating an accelerated hydrogen binding process . Furthermore, the two‐fold increase of exchange current density of NMS‐15 (4.0 mA cm −2 ) as compared to MoSe 2 (1.2 mA cm −2 ) implies the intrinsic activity enhancement in acidic media (Figure S9, Supporting Information) . NMS‐15 also delivers higher ECSA (5.84 mF cm −2 ) than MoSe 2 (2.64 mF cm −2 ) (Figure c, Figure S10 in Supporting Information).…”

Construction of CoP/NiCoP Nanotadpoles Heterojunction Interface for Wide pH Hydrogen Evolution Electrocatalysis and Supercapacitor

“…This is due to the upshift of d-band center of H* capture sites from the Fermi level after elimination of terminal P atoms (Figure 7b). [16,43] So the H 2 O adsorption energy (∆E H2O ) was further calculated. Bader charge analysis results reveal that the average valence charge of surface P atoms in NiCoP decreases from −0.32 to −0.33 after the introduction of Co atoms (the negative Bader charge corresponds to electronic accumulation), in agreement with XPS results above.…”

Ni(OH)2‐WP Hybrid Nanorod Arrays for Highly Efficient and Durable Hydrogen Evolution Reactions in Alkaline Media

“…Generally,t hey suffer from ah igh overpotential in alkaline solutionso wing to the high energy barrier resulting from the sluggish HER kineticsi na lkaline media. [31] Because of the stronga dsorptiono ft he formed OH À on the surfacei na lkaline solutions, the activated water dissociation energy barrier for the WP edge sites becomes very high, contributing to the sluggishH ER kinetics. [30] However,t he Heyrovsky and Volmer steps have different reactives peciesi na cidic (H 3 O + )a nd alkaline( H 2 O/OH À )m edia, and the activated water dissociation steps for most catalysts in alkaline media are usually much slower than those in acidic solutions.…”