Bifunctional Atomically Dispersed Ruthenium Electrocatalysts with Ultralow Metal Loading for Efficient Bipolar Membrane Water Electrolysis

Atomically dispersed catalysts (ADCs) have recently drawn considerable interest for use in water electrolysis to produce hydrogen, because they allow for maximal utilization of metal species, particularly the expensive and scarce platinum group metals. Herein, we report the electrocatalytic performance of atomically dispersed ruthenium catalysts (Ru ADCs) with ultralow Ru loading (0.2wt%), which is prepared by impregnating RuCl 3 precursors onto ammonium salt modified carbon support, followed by high-temperature pyrolysis. The as-obtained Ru ADCs (Ru (0.2)-NC) are active for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which only require a low overpotential ( η ) of 47.1 and 72.8 mV to deliver 10 mA cm -2 for HER in 0.5 M H 2 SO 4 and 1.0 M KOH, respectively, and of 300 mV for OER in 1.0 M KOH, showing favorable bifunctionality. More impressively, the turnover frequency (TOF) of Ru (0.2)-NC is as high as 11.5 s -1 at η=100 mV for HER and 4.89 s -1 at η=300 mV for OER in 1.0 M KOH, demonstrating that the catalysts are intrinsically active. Density functional theory (DFT) calculations reveal that the Ru-N bonding plays an important role in lowering the energy barrier of the reactions, boosting the HER and OER activities. Furthermore, the overall water electrolysis performance is investigated in acid-alkaline dual electrolytes separated by a bipolar membrane (BPM) in the forward-bias configuration, using the bifunctional Ru (0.2)-NC as both HER and OER catalysts. The BPM water electrolysis can afford 10mA cm -2 under a low cell voltage of only 0.89V, and does not show any performance decay upon 100-h continuous operation, showing great potential for energy-saving hydrogen production