The Role of Sodium Sulfate Supporting Electrolyte in Ammonium Transport and Reduction at Interface Between Platinum Cathode and Solution

Ammonium is a potential hydrogen fuel and can be recovered from high ammonium wastewater via electrodeionization (EDI) process. Since NH4+ is a weak acid ion, sodium sulfate (Na2SO4) is used as a supporting electrolyte to improve electrolyte’s conductivity. This manuscript investigated the NH4+ behaviors in high Na2SO4 solution through electrochemical analysis methods and molecular dynamics (MD) simulations. Ionic strength increased, leading to a decreased ionic activity, and thus negatively influenced NH4+ transportation with the increasing concentration of Na2SO4 solution. Na+ competitively occupied the place of electric double layer (EDL) and impeded NH4+ to get closer to the electrode surface. Besides, water molecules played a critical role in determining the net charge density and the potential drop. The experimental tests and theoretical simulation demonstrated that NH4+ reduction (NH4(aq)+ + e- → 0.5 H2(g) + NH3(g)) in the cathode was strengthened in the low concentration range (0-0.25 M Na2SO4) but inhibited in the concentration range of 0.5-1.5 mol L-1.