context: To further improve the purity of as-obtained H2 gas, a stir-bar was also added inside the electrolyser, and after the ORR continued for ∼50 min with magnetic stirring at a cell voltage of 0.55 V, the residual O2 gas attached in the corners or dissolved in the electrolytes can effectively be removed; there was no obvious O2 residual peak detected from the GC. Also, the residual O2 gas can simply be removed by degassing the system with a vacuum pump. However, extra energy is required for such a process.