The clean sole combustion product of H2 (water), has caused H2 to emerge as a critical vector for green energy future in replacement of current fossil fuels. However, the application of H2 as a fuel and/or energy carrier is limited by its transportation and storage issue due to its high flammability and gaseous properties under ambient conditions. To tackle this, NH3 has been suggested as one of the most promising energy carriers for H2 owing to its liquid properties at room temperature and 10 bar, as well as greater hydrogen content compared to H2 itself (per unit volume). Moreover, the readily available regulations and infrastructure for NH3 handling and transportation aids the facilitation of global hydrogen economy (also referred as Hydrogen 2.0). As such, the electrochemical conversion of NOx (including NO3- and NO2-) to ammonium using renewable energy is emerging as a green alternative pathway for the decarbonization of high emission industry to meet net zero emission targets. The key to efficient NOx electrolysis relies on the developing novel yet simple and inexpensive catalysts to improve its performance to enable dynamic renewable integration of small scale, decentralized green ammonia production. Understanding the surface chemistry to establish the structure-activity relationships is of utmost importance to enable future scaleup of this process. In this work, we have undertaken a mechanistic investigation to tune the surface oxidation state of CuOx on Cu foam, and study its impact on conversion of NOx to ammonium (NH4+). Supported by suits of characterization tests, we reveal the importance of tuning Cu oxidation state to maximize Cu2O formation, which forms beneficial Cu2O/Cu interfaces during reaction, allowing enhanced NH4+ yield. To this end, a promising production rate of 45 nmols-1cm-2 and Faradaic efficiency (FENH4+) of 83% at -0.5 V vs RHE are produced.

Engineering CuOx nanoparticles on Cu foam for acidic nitrate reduction to ammonium

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