An electrochemically fabricated cobalt iron oxyhydroxide bifunctional electrode for an anion exchange membrane water electrolyzer

For an anion exchange membrane water electrolyzer (AEMWE), exploring bifunctional electrodes with low cost and high efficiency is a crucial task for future renewable energy systems. Herein, we report a simple method to fabricate cobalt iron oxyhydroxide (Co_<i>z</i>Fe_1-<i>z</i>O_<i>x</i>H_<i>y</i>) bifunctional electrodes for AEMWEs. The bifunctional electrodes were prepared <i>via</i> one-pot electrodeposition on Ti paper (TP). By adjusting the electrodeposition conditions, the morphology and composition of Co_<i>z</i>Fe_1-<i>z</i>O_<i>x</i>H_<i>y</i>/TP could be controlled. The Co₆₅Fe₃₅O_<i>x</i>H_<i>y</i>/TP electrode demonstrated the highest activity for overall water electrolysis owing to the maximized synergy effect between Co and Fe. The bifunctional activities of Co₆₅Fe₃₅O_<i>x</i>H_<i>y</i>/TP were well retained at -50 and 50 mA cm^-2 for 12 h. Co₆₅Fe₃₅O_<i>x</i>H_<i>y</i>/TP, which shows the highest bifunctional activity, was employed in an AEMWE single cell as the anode and cathode. The AEMWE single cell employing Co₆₅Fe₃₅O_<i>x</i>H_<i>y</i>/TP showed a current density of 0.605 A cm^-2 at a cell voltage of 2.0 V_cell. The calculated energy efficiency of the single cell is 55.7% at 2.0 A cm^-2, which is comparable with those of the state-of-the-art AEMWE single cells with bifunctional electrodes. Furthermore, the cell voltage of the single cell with Co₆₅Fe₃₅O_<i>x</i>H_<i>y</i>/TP showed negligible degradation for 50 h at 0.6 A cm^-2.