Surface coating accelerates cathode development for next-generation anion exchange membrane water electrolysis

The conversion and storage of sustainable energy is essential in addressing the global energy and environmental crises. Hydrogen, a clean and abundant energy carrier, plays a pivotal role in decarbonizing energy sectors. Anion exchange membrane water electrolysis (AEMWE) has gained attention due to cost-effective membranes and non-precious-metal electrocatalysts at the anode. However, a significant challenge remains in the hydrogen evolution reaction (HER) under alkaline conditions, as it has significantly lower activity compared to acidic environments. The electrode-electrolyte interface is crucial in overcoming this challenge. It directly impacts system efficiency, stability, and longevity.

As a result, recent studies have frequently underscored the importance of interfacial regulators, particularly the application of surface coatings, as an effective strategy to enhance HER activity.1,2,3,4 These coatings, which may consist of diverse materials such as organic polymers, metal oxides, or phosphates, can improve the catalytic properties of the electrode by optimizing its interaction with H2O, thus facilitating the reaction and reducing the energy barriers involved. Furthermore, surface coatings can play a vital role in mitigating undesirable effects, such as catalyst oxidation and poisoning, thereby enhancing the long-term stability and durability of the electrodes.

Overcoming the sluggish alkaline HER kinetics

Unlike acidic environments, where hydrogen ions are readily available, the alkaline HER requires H2O dissociation before hydrogen adsorption and recombination, introducing a substantial kinetic barrier. This step significantly reduces reaction rates, often resulting in performance that is several orders of magnitude lower than under acidic conditions. Consequently, optimizing the kinetics of H2O dissociation and ensuring efficient proton supply to the active sites are paramount for enhancing cathode performance.

Surface coatings have emerged as powerful tools to address this kinetic bottleneck by tailoring the local chemical environment at the electrode-electrolyte interface. A landmark example is the design of Pt@Ni(OH)2 core-shell nanoparticles.1 As depicted in Figure 1A, this structure features a crystalline Pt tetrahedral core encapsulated within an amorphous Ni(OH)2 shell. The amorphous Ni(OH)2 shell serves a dual role, functioning as both a H2O dissociation catalyst and a proton-conductive layer that ensures a continuous proton supply to the active Pt sites. This results in a proton-enriched local environment, which shifts the HER kinetics toward an acidic-like, Tafel-step-limited pathway. Furthermore, structural analysis confirms that the tetrahedral shape and core-shell structure of Pt@Ni(OH)2 is well-maintained, while the Ni(OH)2 shell effectively repels impurity ions and slows down the dissolution and diffusion of Pt atoms from the catalyst surface.