All CCMs were preconditioned by soaking in KOH(aq) (1 M) at least 24 h before cell assembly. The KOH(aq) solution was refreshed twice during preconditioning to ensure both membrane and ionomer were converted to the hydroxide form prior to testing. Following cell assembly and installation in the flow setup, KOH(aq) (1 M) feed solution was circulated for 20 min to heat the cell to 40 °C. The CCM was conditioned by stepping the current from 0.1 to 1 A cm -2 in 0.1 A cm -2 steps, holding for 2 min at each step.