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

Abstract

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.