Ammonium as a sustainable proton shuttle in bioelectrochemical systems

► A novel way of overcoming the bottleneck of slow proton flux in BES is described. ► Ammonia addition to the anode prevented acidification and enabled proton transfer. ► Ammonia could be recovered from the cathode and continuously recycled to the anode. ► Ammonia recycle allowed long term sustainable operation of the cell. ► Using ammonium as proton shuttle prevented cation accumulation in the catholyte.