Microbial electrolysis cell (MEC): Strengths, weaknesses and research needs from electrochemical engineering standpoint

•Thermodynamic basics of MEC are revisited.•Equilibrium cell voltage of 0.123 V and maximum energy yield of 10 are main advantages.•Faradaic yields can help identifying various MEC malfunctioning.•Adding salts to increase the electrolyte ionic conductivity exacerbates pH issues.•Local pH gradients and ion migration form a negative feedback loop.