Engineering copper supported mixed manganese oxides as selective bimetallic electrocatalyst for nitrate to ammonia conversion at environmentally relevant concentrations

Anthropogenic activities have severely disrupted the natural nitrogen cycle, resulting in increasing NO3- pollution in environmental waters. The electrochemical reduction of nitrate (ERN) may provide a remediation strategy via a highly selective pathway for pollution conversion into a profitable chemical – NH3. Platinum group materials (PGMs) have limited the adoption of ERN technologies due to their high prices and sparse earth abundance. Herein we have developed a highly active copper supported, nano manganese mixed oxides (Cu/MnM) for the selective electrochemical reduction of NO3- into NH3. The optimized synthesis achieved 91 % conversion of a 30 mg-N L−1 NO3- solution within 60 minutes of galvanostatic ERN treatment highlighting the rapid NO3- conversion kinetics of the Cu/MnM electrocatalyst. At optimized conditions the Cu/MnM electrocatalyst achieved an 86 % selectivity for NH3 generation for 60 minutes of ERN treatment, showcasing highly efficient ammonia electrogeneration. Both applied current and initial NO3- concentration was observed to affect performance. Cycling studies revealed stable electrode performance over 10 consecutive ERN cycles, highlighting a stable electrocatalyst design. The work presented provides a paradigm shift for engineering low-cost earth abundant mixed metal oxide catalytic structures which rival PGMs performance, under scalable operational conditions. [Display omitted] •Rapid NO3- conversion and NH3 selectivity were achieved.•A direct charge transfer mechanism was identified to drive NH3 electrosynthesis.•Both applied current and initial NO3- concentrations greatly impact ERN performance.•Selective reduction achieved with earth abundant low-cost metals.