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 NH 4 + is a weak acid ion, sodium sulfate (Na 2 SO 4 ) is used as a supporting electrolyte to improve electrolyte’s conductivity. This manuscript investigated the NH 4 + behaviors in high Na 2 SO 4 solution through electrochemical analysis methods and molecular dynamics (MD) simulations. Ionic strength increased, leading to a decreased ionic activity, and thus negatively influenced NH 4 + transportation with the increasing concentration of Na2 S O 4 solution. Na + competitively occupied the place of electric double layer (EDL) and impeded NH 4 + 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 NH 4 + reduction ( NH 4(aq) + + e - → 0.5 H 2(g) + NH 3(g) ) in the cathode was strengthened in the low concentration range (0-0.25 M Na 2 SO 4 ) but inhibited in the concentration range of 0.5-1.5 mol L -1 .