Band Energy Modulation in an Fe–Mn–ZnO Nanowire–Nanosheet Catalyst for Efficient Overall Water Splitting

Here, we studied a simple, scalable, and in situ hydrothermal method to prepare an Fe–Mn-doped ZnO nanowire–nanosheet on a three-dimensional (3D) Ni-foam substrate for electrocatalytic overall water splitting. Attractively, the doping of Fe and Mn in ZnO plays a significant role in mobilizing the electron from Fe and Mn toward ZnO in the Fe–Mn-doped ZnO nanowire–nanosheet due to different vacuum levels of Fe, Mn, and ZnO, facilitating the development of more active sites on the surface of the catalyst, which plays a crucial role in improving the catalytic performances during overall water splitting. Consequently, the Fe–Mn-doped ZnO nanowire–nanosheet shows a lowermost overpotential of 230 mV and a lowermost Tafel slope of 115.2 mV dec–1 during the hydrogen evolution reaction (HER) and 248 mV overpotential and a short Tafel slope of 109.1 mV dec–1 during the oxygen evolution reaction (OER) in a 1.0 M KOH electrolyte. Besides, the Fe–Mn-doped ZnO nanowire–nanosheet depicts low charge transfer and series resistances of 3.7 and 0.41 Ω during the HER and 0.36 and 1.66 Ω during the OER, respectively. Also, it elucidates outstanding durability at −10 mA cm–2 for 12 h (HER) and 10 mA cm–2 for 12 h (OER) using chronopotentiometry and 1000 cycles. In addition, the Fe–Mn–ZnO||Fe–Mn–ZnO nanowire–nanosheet cell shows a lower potential of 1.74 V and outstanding stability over 24 h to deliver 10 mA cm–2 in electrocatalytic overall water splitting. Besides, the staircase stability of the Fe–Mn–ZnO||Fe–Mn–ZnO nanowire–nanosheet cell also suggests outstanding stability over 8.2 h at different current densities. Captivatingly, the concept of energy band modulation in the bimetallic doped Fe–Mn–ZnO nanowire–nanosheet catalyst is envisaged to explore insights into the mechanisms of the evolution of hydrogen and oxygen.