This work examines a pH control method using ammonium (NH4+) as a sustainable proton shuttle in a CEM-equipped BES. Current generation was sustained by adding NH3 or ammonium hydroxide (NH4OH) to the anolyte, controlling its pH at 7. Ammonium ion migration maintained the catholyte pH at approximately 9.25. Such NH4+/NH3 migration accounted for 90±10% of the ionic flux in the BES. Reintroducing the volatilized NH3 from the cathode into the anolyte maintained a suitable anolyte pH for sustained microbial-driven current generation. Hence, NH4+/NH3 acted as a proton shuttle that is not consumed in the process.