Influence of PAA coating on three-electrode electrochemical properties. Electrodes used were CCF-GP loaded by activated carbon YP-50, with and without PAA coating, some additionally modified by YP-50’s preoxidation (M-YP-50). (a) CV curves scanned at 2 mV s-1, for YP-50-CCF-GP electrode in 0.5 M H2SO4 (label: H2SO4) and 2 M Li2SO4 (label: Li2SO4, pH~6), and PAA-coated YP-50-CCF-GP electrode in 2 M Li2SO4 (label: PAA-Li2SO4, pH~6). (b) Same as (a) for PAA-coated YP-50-CCF-GP electrode in 2 M Li2SO4 adjusted to several pH. (c) Tafel plots of electrode potential against pH at steady-state current density of 10 μA cm-2, for YP-50-CCF-GP, and PAA-coated/uncoated M-YP-50-CCF-GP electrodes. (d) Potential for hydrogen evolution reaction and oxygen evolution reaction of uncoated (blue) and coated (red) CCF-GP electrodes in 2 M Li2SO4 electrolyte, adjusted to various pH. Shadowed band is a theoretical electrochemical window of water. Same electrode/electrolyte combinations as in (a) for (e) rate performance of specific capacity according to the galvanostatic charging/discharging test from 0.5 to 40 A g-1, and (f) specific capacity versus square root of half-cycle time according to CV test data from 2 to 500 mV s-1. Extrapolated intercept capacity is rate-independent capacity, the remainder diffusion-controlled capacity.