Charge allocation and mass transfer efficiency during hydrogen evolution reaction in high salinity neutral...

Area of Science:

• Electrochemistry
• Materials Science
• Environmental Engineering

Background:

• High-salinity wastewater presents a sustainable source for hydrogen production, crucial for carbon neutrality goals.
• Complex matrix effects in neutral electrolytes create unfavorable interfacial microenvironments, hindering efficient hydrogen evolution reaction (HER).
• Understanding electrolyte matrix influences on HER mechanisms is vital for optimizing hydrogen production from challenging feedstocks.

Purpose of the Study:

• To systematically investigate the charge allocation and mass transfer mechanisms of HER in different electrolyte matrices (sulfate, nitrate, chloride).
• To elucidate the role of electrode porosity and electrolyte composition in HER performance using nickel foam electrodes.
• To provide a mechanistic understanding for optimizing hydrogen production from high-salinity wastewater.

Main Methods:

• Electrochemical characterization of hydrogen evolution reaction (HER) using nickel foam (NF) electrodes with varying porosity (e.g., 80 PPI NF).
• Systematic investigation of distinct electrolyte matrices: Na₂SO₄, NaNO₃, and NaCl.
• Density Functional Theory (DFT) calculations to analyze electronic interactions between electrolyte anions and Ni (111) surfaces.

Main Results:

• 80 PPI NF electrodes showed superior HER activity due to abundant active sites and in-situ active species promoting water dissociation.
• The Na₂SO₄ system achieved optimal performance with 93.8% Faradaic efficiency (FE) and excellent durability (96.8% yield) due to minimal kinetic competition.
• NaNO₃ was hindered by nitrate electro-reduction, while NaCl suffered degradation (FE dropped to 66.7%) from chlorine redox shuttling and electrode etching. DFT confirmed SO₄^2- had minimal impact, while Cl^- negatively affected Ni (111) electronic structure.

Conclusions:

• Electrolyte matrix composition significantly dictates HER efficiency and electrode stability in high-salinity wastewater.
• Sulfate electrolytes provide a favorable environment for HER by minimizing parasitic reactions and electronic perturbations on the nickel electrode.
• These findings offer a mechanistic basis for optimizing charge allocation and electrode design for efficient hydrogen generation from saline sources.