Growth of One-Dimensional RuO₂ Nanowires on g-Carbon Nitride: An Active and Stable Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution Reactions at All pH Values

Development of highly efficient and durable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER) is essential for efficient solar fuel generation. The commercial RuO₂ or RuO₂-based catalysts are highly active toward OER, but their poor stability under different operating conditions is the main obstacle for their commercialization. Herein, we report growth of one-dimensional highly crystalline RuO₂ nanowires on carbon nitride (1D-RuO₂-CNx) for their applications in HER and OER at all pH values. The 1D-RuO₂-CNx, as an OER catalyst, exhibits a low onset overpotential of ∼200 mV in both acidic and basic media, whereas Tafel slopes are 52 and 56 mV/dec in acidic and basic media, respectively. This catalyst requires a low overpotential of 250 and 260 mV to drive the current density of 10 mA cm⁻² in acidic and basic media, respectively. The mass activity of 1D-RuO₂-CNx catalyst is 352 mA mg⁻¹, which is ∼14 times higher than that of commercial RuO₂. Most importantly, the 1D-RuO₂-CNx catalyst has remarkably higher stability compared to commercial RuO₂. This catalyst also exhibits superior HER activity with a current density of 10 mAcm⁻² at ∼93 and 95 mV in acidic and basic media. The HER Tafel slopes of this catalyst are 40 mV/dec in acidic condition and 70 mV/dec in basic condition. The HER activity of this catalyst is slightly lower than Pt/C in acidic media, whereas in basic media it is comparable or even better than that of Pt/C at higher overpotentials. The HER stability of this catalyst is also better than that of Pt/C in all pH solutions. This superior catalytic activity of 1D-RuO₂-CNx composite can be attributed to catalyst-support interaction, enhanced mass and electron transport, one-dimensional morphology, and highly crystalline rutile RuO₂ structure.