Low-Cost, High-Yield Zinc Oxide-Based Nanostars for Alkaline Overall Water Splitting

The investigation of high-efficiency and sustainable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media is critical for renewable energy technologies. Here, we report a low-cost and high-yield method to obtain ZnOHF-ZnO-based 2D nanostars (NSs) by means of chemical bath deposition (CBD). The obtained NSs, cast onto graphene paper substrates, were used as active materials for the development of a full water splitting cell. For the HER, NSs were decorated with an ultralow amount of Pt nanoparticles (11.2 μg cm^-2), demonstrating an overpotential of 181 mV at a current density of 10 mA cm^-2. The intrinsic activity of Pt was optimized, thanks to the ZnO supporting nanostructures, as outlined by the mass activity of Pt (0.9 mA mg_Pt^-1) and its turnover frequency (0.27 s^-1 for a Pt loading of 11.2 μg cm^-2). For the OER, bare NSs showed a remarkable result of 355 mV at 10 mA cm^-2 in alkaline media. Pt-decorated and bare NSs were used as the cathode and anode, respectively, for alkaline electrochemical water splitting, assessing a stable overpotential of 1.7 V at a current density of 10 mA cm^-2. The reported data pave the way toward large-scale production of low-cost electrocatalysts for green hydrogen production.