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.
Deep eutectic solvents (DESs) are promising media for CO2 electroreduction because of their high CO2 solubility, low cost, and eco-friendliness. However, the high viscosity and poor ionic conductivity severely limit their applications. In this study, low-viscosity polar aprotic solvents, propylene carbonate (PC) and sulfolane (SL), were used as diluents in Ethaline (ChCl:2EG) to prepare mixed electrolytes for electrochemical CO2 reduction. Raman and infrared spectra indicate that PC and SL can participate in the eutectic network of Ethaline through intermolecular hydrogen bonding, thereby decreasing the viscosity. The current density of the Ag cathode increases from 1.7 to 8.0 and 5.3 mA/cm2 with the addition of PC and SL, respectively. The two diluents also result in improved CO faradaic efficiency (FECO) and suppressed HER because the C═O and S═O bonds in the molecular frameworks of PC and SL can disrupt the hydrogen bonds of accumulated water molecules during electrolysis. At −2.0 V, FECO increases from 63% to over 90% upon the addition of PC and SL. This study provides new insights into the design of high-performance DES electrolytes for CO2 electroreduction.
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