Electrochemical Kinetics of Hydrogen Evolution Reactions

The hydrogen evolution reaction (HER) is a cornerstone of sustainable energy technologies, underpinning water electrolysis for green hydrogen production. At its heart lie sequential proton‐electron transfer events that determine the overall reaction rate, conventionally described as the Volmer (proton adsorption), Heyrovsky (electrochemical desorption) and Tafel (recombination) steps. The kinetics of these elementary processes are influenced by catalyst composition, surface morphology, electrolyte pH and mass transport. Key performance metrics include the exchange current density, which reflects intrinsic activity at equilibrium, and the overpotential required to drive a given current density. Detailed mechanistic insight is obtained through analysis of Tafel slopes, microkinetic modelling and in situ characterisation of adsorbed intermediates. Recent advances have emphasised the interplay between surface coverage of hydrogen intermediates and electron‐transfer barriers, challenging traditional applications of the Butler–Volmer formalism. Beyond fundamental studies, optimisation strategies focus on tailoring electronic structure and nanostructure to lower kinetic barriers, while mitigating mass‐transport limitations at high rates. The global imperative to decarbonise energy systems has propelled HER research to the forefront, with practical applications spanning large‐scale electrolyser design, off‐grid renewable integration and distributed hydrogen refuelling stations.

Research from Nature Portfolio

Recent studies have provided a rigorous microkinetic framework for aqueous HER, demonstrating that observed Tafel slopes vary with surface coverage of adsorbed hydrogen rather than adhering to simplistic limiting‐coverage assumptions. By mapping coverage‐dependent slopes to specific elementary steps, these analyses have yielded quantitative benchmarks for identifying rate‐determining processes on metal and alloy catalysts. Furthermore, the work highlights the limitations of the conventional Butler–Volmer equation when applied in isolation, calling for integrated models that couple adsorbate thermodynamics with electron‐transfer kinetics. This foundational insight has reshaped the interpretation of electrochemical measurements and guided the design of next‐generation electrocatalysts with tailored adsorption energies.

Electrochemical Kinetics of Hydrogen Evolution Reactions publication trend

The graph below shows the total number of articles in electrochemical kinetics of hydrogen evolution reactions across all publications each year (not limited to Nature Index journals).

Technical terms

Tafel slope: The gradient of the overpotential versus log(current density) plot, indicative of the rate‐determining step in an electrocatalytic reaction.

Overpotential: The additional potential beyond the thermodynamic equilibrium voltage required to drive an electrochemical reaction at a desired rate.

Exchange current density: The current density at zero overpotential, reflecting the intrinsic catalytic activity under equilibrium conditions.

Volmer step: The initial adsorption of a proton and electron onto the electrode surface to form an adsorbed hydrogen intermediate.

Heyrovsky step: The electrochemical desorption of adsorbed hydrogen, combining a proton, electron and surface‐bound hydrogen to form H₂.

Butler–Volmer equation: A fundamental kinetic expression relating electrode current to overpotential, proton concentration and charge‐transfer coefficients.

References

1. Optimizing hydrogen production by alkaline water decomposition with transition metal-based electrocatalysts. Environmental Chemistry Letters (2023).
2. Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversion. Scientific Reports (2015).
3. Grain Boundary—A Route to Enhance Electrocatalytic Activity for Hydrogen Evolution Reaction. Applied Sciences (2022).