Electrochemical reduction of NO3− to NH3 using defect-rich TiO2 support loaded with CuNi catalysts: differential electrochemical mass spectrometry insights

A promising approach for reducing nitrate (NO3−) in water waste is NO3− reutilization to ammonia (NH3). This work investigates the synergistic effect of Cu40Ni60 catalyst on a defect-rich TiO2 (TNSD) carbon vulcan composite (C-TNSD). The study starts with CuNi metallic content pre-screened over carbon vulcan (C) to identify the most promising CuNi ratios for nitrate reduction reaction (NO3-RR) to NH3. This is the case of Cu 20 wt% and Ni 80 wt% (Cu20Ni80), Cu 40 wt% and Ni 60 wt% (Cu40Ni60), Cu 60 wt% and Ni 40 wt% (Cu60Ni40), and Cu 80 wt%, Ni 20 wt% (Cu80Ni20) and Cu/Ni monometallic catalysts. Among these ratios, Cu40Ni60 resulted in the most promising electrocatalyst when loaded over C-TNSD, whose functionality has been assessed using in situ differential electrochemical mass spectrometry (DEMS). The results indicate that Cu40Ni60/C-TNSD attains a similar NH3 selectivity to Cu40Ni60 supported on TiO2-carbon vulcan composites. However, Cu40Ni60/C-TNSD does not hinder charge transport, making it the most suitable electrocatalyst for NH3 production. A synergistic interaction between Cu40Ni60 and C-TNSD is proposed. The results are supported by structural, (electro)chemical, and morphological characterization. From a broader perspective, defective-rich catalysts can be developed to control the electrochemical reaction sequence during NO3-RR.