UC Santa Cruz

Electrochemical water splitting provides promising technology for green hydrogen production. Among different electrolysis technologies, alkaline water splitting is attractive because it can use earth-abundant electrode materials and relatively low-cost materials. However, efficient operation at industrially relevant current densities remains challenging due to gas bubble accumulation, ion-transport resistance, sluggish anodic kinetics. These limitations become more severe under high-rate conditions, where rapid gas generation and fast ionic consumption can reduce electrode-electrolyte contact and increase the overall cell voltage.This dissertation focuses on advanced electrode design and interfacial engineering strategies to address these challenges. First, nickel nanocone-modified surfaces were developed to improve gas bubble detachment. The nanocone structures created a superaerophobic interface, leading to shorter bubble residence times and smaller bubble detachment sizes during both the hydrogen evolution reaction and oxygen evolution reaction. Simulations and high-speed imaging confirmed that the nanocone geometry reduced bubble adhesion and promoted rapid gas release. Consequently, nanocone-modified nickel foil, foam, and 3D-printed lattice electrodes showed reduced overpotentials at high current densities, and a two-electrode device using nanocone-modified lattice electrodes operated stably for up to100 h.Second, a 3D-printed interpenetrating gyroid electrode architecture was designed to improve ion transport. This structure consists of two independent but spatially interwoven electrode networks, reducing the interelectrode distance while maintaining ordered channels for electrolyte transport. Simulations showed more uniform ion concentration profiles and smoother electric potential gradients than separated gyroid electrodes. Electrochemical measurements further revealed lower solution and charge-transfer resistances, confirming improved ionic transport and reaction accessibility. The architecture also maintained stable long-term operation and could be combined with catalyst modification to enhance water-splitting activity.Finally, urea electrooxidation was investigated as an alternative anodic reaction to replace oxygen evolution for more energy-efficient hydrogen production. A valence-state engineering strategy was developed through controlled sulfurization to form nickel sulfide catalysts with enriched Ni3+ species, which are recognized as the active sites for the urea oxidation. The optimized nickel sulfide catalyst exhibited enhanced urea oxidation activity compared with nickel hydroxide. The results showed that sulfurization modulated the Ni3+/Ni2+ ratio and catalytic surface environment, facilitating charge transfer and lowering the energy barrier for C-N bond cleavage. The catalyst was further integrated into a 3D-printed interpenetrating electrode device and evaluated under flow-cell conditions.Overall, this dissertation demonstrates that surface morphology, electrode architecture, catalyst chemistry, and device configuration must be jointly optimized to improve high-rate alkaline water splitting. By addressing gas bubble accumulation, ion-diffusion limitations, and anodic energy loss, this work provides practical design principles for efficient and stable electrochemical hydrogen production under industrially relevant conditions.