Electrochemical Nitrate-to-Ammonia Conversion Enabled by Carbon-Decoration of Ni─GaOOH Synthesized via Plasma-Assisted CO2 Reduction.

Abstract

The release of nitrates into the environment leads to contaminated soil and waterthat poses a health risk to humans and animals. Due to thetransition to renewable energy-based technologies, an electrochemical approach is an emerging option that can selectively produce valuable ammonia from nitrate sources. However, traditional metal-based electrocatalysts often suffer from low nitrate adsorption that reduces NH3 production rates. Here, aNi-GaOOH-C/Ga electrocatalyst for electrochemical nitrate conversion into NH3 is synthesized via a low energy atmospheric-pressure plasma process that reduces CO2 into highly dispersed activated carbon on dispersed Ni─GaOOH particles produced from a liquid metal Ga─Ni alloy precursor. Nitrate conversionrates of up to 26.3µgh-1 mg-1 cat areachieved with good stability of up to 20h. Critically, the presence of carbon centers is central to improved performance whereboth Ni─C and NiO─C interfaces act as NO3- adsorption and reduction centers during thereaction. Density functional theory (DFT) calculations indicate that the NiO─C and Ni─C reaction sites reduce the Gibbs free energy required for NO3- reduction to NH3 compared to NiO and Ni. Importantly, catalysts without carbon centers do not produce NH3 , emphasizing the unique effects of incorporating carbon nanoparticles into the electrocatalyst.