Electrochemical reconstruction of non-noble metal-based heterostructure nanorod arrays electrodes for highly stable anion exchange membrane seawater electrolysis

Direct seawater electrolysis for hydrogen production has been regarded as a viable route to utilize surplus renewable energy and address the climate crisis. However, the harsh electrochemical environment of seawater, particularly the presence of aggressive Cl−, has been proven to be prone to parasitic chloride ion oxidation and corrosion reactions, thus restricting seawater electrolyzer lifetime. Herein, hierarchical structure (Ni,Fe)O(OH)@NiCoS nanorod arrays (NAs) catalysts with heterointerfaces and localized oxygen vacancies were synthesized at nickel foam substrates via the combination of hydrothermal and annealing methods to boost seawater dissociation. The hierarchical nanostructure of NiCoS NAs enhanced electrode charge transfer rate and active surface area to accelerate oxygen evolution reaction (OER) and generated sulfate gradient layers to repulsive aggressive Cl−. The fabricated heterostructure and vacancies of (Ni,Fe)O(OH) tuned catalyst electronic structure into an electrophilic state to enhance the binding affinity of hydroxyl intermediates and facilitate the structural transformation into amorphous γ-NiFeOOH for promoting OER. Furthermore, through operando electrochemistry techniques, we found that the γ-NiFeOOH possessing an unsaturated coordination environment and lattice-oxygen-participated OER mechanism can minimize electrode Cl− corrosion enabled by stabilizing the adsorption of OH* intermediates, making it one of the best OER catalysts in the seawater medium reported to date. Consequently, these catalysts can deliver current densities of 100 and 500 mA cm−2 for boosting OER at minimal overpotentials of 245 and 316 mV, respectively, and thus prevent chloride ion oxidation simultaneously. Impressively, a highly stable anion exchange membrane (AEM) seawater electrolyzer based on the non-noble metal heterostructure electrodes reached a record low degradation rate under 100 μV h−1 at constant industrial current densities of 400 and 600 mA cm−2 over 300 hours, which exhibits a promising future for the non-precious and stable AEMWE in the direct seawater electrolysis industry.