Structure evolution of OTQC at different states of charge was performed on composite electrodes cycled in 3 M ZnSO4 (Figure ). At the lowest voltage, flakes of several micrometers in size were observed throughout the surface of discharged electrodes (Figure ). These deposits are most likely salt by-products formed due to the increased local pH after H + insertion into the OTQC electrode, as was reported recently. To support this claim, EDS mapping was performed (Figure ). The presence of sulfur and zinc was detectable on the surface, with areas of increased Zn, S, and O concentration matching, indicating the formation of inorganic deposits. The findings further support the H + insertion as seen from the ex-situ FT-IR spectrum of the discharged electrode. Similarly to electrodes cycled in Li-based electrolyte, the overall structural integrity of the electrode seems to be maintained even after prolonged cycling, with no detectable deterioration of the contact between active particles and carbon black (Figure ).