Optimizing rod-shaped anode configuration in ultra-high-current-density seawater electrolysis for scalable hydrogen production

Growing concern over the environmental impact of fossil fuels has intensified efforts to develop sustainable routes for hydrogen production. Seawater electrolysis powered by renewable energy offers a particularly attractive option because of seawater's abundance and high ionic conductivity. Yet, its progress has been limited by the tendency of the chlorine evolution reaction (CER) to dominate over the oxygen evolution reaction (OER), leading to chlorine generation and associated environmental hazards. In our previous work, we showed that operating at high current densities ( J c > 10 A cm −2 ) with consumable graphite rod-shaped electrodes can effectively suppress CER. Building on that foundation, the present study examines how hydrogen production performance changes with the number and configuration of rod-shaped anodes used with a single cathode. Through a combination of experiments and two-dimensional finite-element modeling, we found that multi-anode configurations can be tuned to enhance hydrogen yield while maintaining full CER suppression. Reducing the electrode spacing from 10 mm to 1 mm increases the local electric field by roughly an order of magnitude, lowering the energy demand from about 0.98 kWh to 0.098 kWh per gram of hydrogen. Accounting for field-enhanced ionic mobility—potentially up to eight-fold for H + ions—further reduces the projected energy cost to near the 0.05–0.06 kWh g −1 H 2 range, approaching the thermodynamic limit. These results demonstrate that electrode geometry and spacing are central to improving efficiency in high-current-density seawater electrolysis.