Solar-rechargeable zinc-nitrate galvanic cell coupled with chemical reduction for self-powered nitrate remediation

Nitrate (NO 3 − ) contamination poses a critical global water security challenge, particularly in remote and off-grid regions where conventional centralized treatment infrastructure is economically impractical. Here, we report a solar-rechargeable zinc-nitrate (Zn-NO 3 − ) galvanic cell that transforms nitrate remediation from an energy-consuming process to a solar-rechargeable, self-powered system. The system works through a successive two-step process. First, a galvanic cell, comprising a Zn anode and an electrochemically reconstructed nanostructured silver (NS@Ag) cathode, spontaneously reduces nitrate (NO 3 − ) to nitrite (NO 2 − ). The first step needs no external power and achieves high nitrite selectivity (>98 %). Then, the generated NO 2 − reacts with sulfamic acid (HSA) to form benign nitrogen gas (N 2 ); this stoichiometric reaction ensures almost complete N 2 selectivity. A key point of our design is the integration of photovoltaics to regenerate the consumed Zn anode using solar energy, which creates a closed, self-sustaining loop. Further tests showed that the system remained stable over long-term cycling, with performance fully recovering after either electrical or solar recharging. By combining galvanic energy harvesting with solar regeneration, this integrated system offers a promising decentralized strategy for nitrate removal in off-grid or resource-poor regions.