CoS₂ needle arrays induced a local pseudo-acidic environment for alkaline hydrogen evolution

Hydrogen production through the hydrogen evolution reaction (HER) is a key area in renewable energy research. In alkaline environments, HER performance is hindered by the slow dissociation of water and the buildup of hydroxide ions near active sites. Prior research has shown that catalyst morphology influences reaction efficiency. However, the role of localized electric fields in mitigating OH⁻ accumulation remains unclear. This gap motivated the investigation of structured catalysts that could modulate the local environment. No prior work had resolved how electric fields affect HER in alkaline settings. The need for stable, efficient catalysts in industrial electrolysis remains unmet. This paper introduces a novel approach using nanoneedle arrays to alter local pH conditions. The study addresses the unresolved challenge of OH⁻ interference in alkaline HER.

The aim of this work is to develop a CoS₂-based catalyst that enhances alkaline HER performance by manipulating the local electric field. The specific problem is the slow H₂O dissociation rate caused by OH⁻ accumulation. The motivation lies in improving HER efficiency for industrial hydrogen production. The authors propose using nanoneedle arrays to generate a stronger electric field. This approach could reduce OH⁻ concentration near active sites. The study seeks to confirm whether electric field modulation improves HER kinetics. The researchers designed a CoS₂ needle array on carbon cloth to test this hypothesis. The goal is to provide a scalable solution for efficient alkaline HER.

The researchers synthesized a CoS₂ needle array on carbon cloth (NAs@C) and compared it with disordered needles (DNs@C). They used finite-element simulations to model the electric field distribution. The simulations revealed that needle arrays create a stronger local electric field (LEF) than disordered structures. The team measured pH changes at the electrode surface to assess OH⁻ concentration. They conducted electrochemical tests to determine HER overpotential and Tafel slope. The experiments were performed in 1 M KOH under standard conditions. The study evaluated the catalyst's performance at 10 mA cm⁻² current density. The methods combined computational modeling with experimental validation.

The NAs@C catalyst showed a HER overpotential of 121 mV at 10 mA cm⁻² in 1 M KOH. The Tafel slope was measured at 59.87 mV dec⁻¹, indicating efficient electron transfer. The local electric field (LEF) generated by the needle arrays repelled OH⁻ ions from active sites. This repulsion created a pseudo-acidic environment with lower OH⁻ concentration. The pseudo-acidic condition promoted faster H₂O dissociation compared to disordered needles. The finite-element simulations confirmed stronger LEF in needle arrays. The lower OH⁻ concentration was verified through pH measurements on the electrode surface. These results suggest that electric field modulation enhances HER performance in alkaline settings.

The authors propose that the local electric field generated by CoS₂ needle arrays reduces OH⁻ accumulation. This pseudo-acidic environment accelerates H₂O dissociation in alkaline HER. The NAs@C catalyst outperformed disordered structures in electrochemical tests. The study supports the idea that nanoneedle arrays can modulate local pH conditions. The results suggest that electric field manipulation is a viable strategy for HER improvement. The findings align with the hypothesis that structured catalysts enhance reaction kinetics. The authors conclude that needle arrays provide a new design principle for alkaline HER catalysts. The work highlights the importance of morphology in electrocatalytic performance.