pH-Universal, High-Performance RuO ₂ Pseudocapacitors Powered by Hydrogen Battery Chemistry

Supercapacitors are at the forefront for powering next-generation electronic devices and offer instantaneous power supply and fast response times. However, the bottleneck lies in designing electrode materials with high capacitance and high energy density. Here, we report a pH-universal RuO 2 -based electrocatalytic hydrogen gas capacitor (EHGC). This innovation marks an important leap in pseudocapacitor technology, enabling exceptional chemical stability and catalytic versatility across a wide pH range. This versatility is ascribed to the robustness of RuO 2 and the catalytic properties of hydrogen electrode, resulting in a hybrid system with superior capacitance and energy density. RuO 2 -EHGC delivers a high capacitance of 626 F/g and an energy density of 57 Wh/kg at a power density of 200 W/kg in the acidic electrolyte, as well as 80 Wh/kg at 459 W/kg in the alkaline electrolyte at a current density of 1 A/g. Furthermore, RuO 2 -EHGC exhibits capacitance retention of 82% after 100,000 cycles at a high current of 30 A/g. The charge storage mechanism is evaluated using ex situ Raman and x-ray photoelectron spectroscopy, which confirms the reversibility of the capacitive charge storage process. This study shows a new approach to the development of high-performance pseudocapacitors, which has the potential to open new avenues of green and sustainable energy storage devices.