Iridium on vertical graphene as an all-round catalyst for robust water splitting reactions

Among all noble metals, Ir has become popular for water reduction/oxidation due to its stability in both acidic and alkaline electrolytes. We find that Ir on vertical graphene (Ir_VG) is an all-round bi-functional catalyst. A high content of metallic Ir (Ir0) manifests as active catalytic sites supported by a superaerophobic vertical graphene surface designed to facilitate two-/four-electron transfer processes. This binder-free, nanoscale hybrid catalyst yields low overpotentials for the HER and OER in both acidic and alkaline media. With a minimal catalyst loading of 50 μg cm−2 for the HER, the catalyst delivers a current density of 10 mA cm−2 at overpotentials of 47 mV and 17 mV in acidic and alkaline media, respectively. For the OER, the catalyst achieves a current density of 10 mA cm−2 at overpotentials of 300 mV and 320 mV in acidic and alkaline media, respectively. This highly active bi-functional catalyst enables total water splitting at 1.58 V (acidic) and 1.57 V (alkaline) for 10 mA cm−2. Unlike other catalysts, Ir_VG shows good stability against corrosion with undiminished current density even at high potential in harsh acidic or alkaline environments over 24 h. This unprecedented, versatile catalyst offers an appealing, cost-effective noble-metal-based scheme for pH-independent water electrolysis.