Other commercial carbon gas diffusion layers did not fulfil these physical requirements for the current flow cell design, see Supplementary Text 2.1. Experiments, unless otherwise stated, were conducted in the electrolyte developed by Li et al. (1 M LiBF4 in diglyme with varying EtOH concentrations). A flow cell with a working area of 4 cm 2 was employed with a Freudenberg H15 cathode, Pt wire pseudo reference electrode and PtAu anode (synthesized as reported by Fu et al. ). Fixed time current pulses were applied, for example: -6 mA cm -2 geo was applied for 30 seconds, then 0 mA cm -2 geo for 120 seconds.