# Enhanced Proton Spillover at Pt‐Cluster/NiO Interface Reduces the Acidic–Alkaline Hydrogen Evolution Activity Gap

## TL;DR

This paper shows how a new catalyst design using platinum nanoclusters on oxygen-deficient nickel oxide improves hydrogen production in both acidic and alkaline conditions.

## Contribution

A new strategy for designing electrocatalysts that narrows the activity gap between acidic and alkaline hydrogen evolution reactions.

## Key findings

- Pt nanoclusters on oxygen-defect-rich NiO nanowires show excellent HER activity and stability.
- Oxygen defects lower the water dissociation energy barrier, enhancing proton spillover and H* coverage.
- The catalyst significantly reduces the activity gap between acidic and alkaline HER compared to commercial Pt/C.

## Abstract

The sluggish hydrogen evolution reaction (HER) kinetics in alkaline media, primarily attributed to the additional water dissociation step, has led to a significant activity gap between acidic and alkaline conditions. Metal‐supported electrocatalysts leveraging hydrogen spillover have garnered significant attention due to sufficiently utilized reaction sites; however, designing active catalysts remains a formidable challenge, primarily due to the limited understanding of the specific regulatory mechanisms governing proton spillover. Herein, a facile strategy is reported for the fabrication of Pt nanoclusters (PtNC) on oxygen‐defect‐rich NiO nanowires (PtNC‐D‐NiO). The electrocatalyst demonstrates excellent intrinsic and mass‐normalized HER activity and remarkable long‐term stability, outperforming PtNC on pristine NiO nanowires and commercial Pt/C. Notably, its alkaline HER activity is fairly close to its acidic counterpart, significantly narrowing the activity gap compared to commercial Pt/C. Advanced ex situ/operando physicochemical characterizations, including in situ electrochemical impedance spectroscopy, reveal that oxygen defects substantially lower the water dissociation energy barrier. This facilitates rapid H* spillover and enhances local H* coverage on PtNC, thus accelerating subsequent H* recombination to boost alkaline HER. This work not only offers a cost‐effective catalyst design strategy but also provides fundamental insights into the role of hydrogen spillover in optimizing electrocatalytic performance.

The integration of Pt nanoclusters onto oxygen‐deficient NiO significantly accelerates both the water dissociation and proton transfer steps via the hydrogen spillover mechanism, thereby narrowing the activity gap between alkaline and acidic hydrogen evolution reactions.© 2026 WILEY‐VCH GmbH