RuN_<i>x</i> clusters anchored on hierarchically porous N-doped carbon spheres for efficient alkaline hydrogen evolution reaction

Carbon-supported Ru clusters have been recognized as promising electrocatalysts for alkaline hydrogen evolution reaction (HER), but their catalytic activity is still limited by the weak metal-carbon interaction or the blockage of active sites. Herein, we report a facile method by which RuN_<i>x</i> clusters are <i>in situ</i> anchored on hierarchically porous N-doped carbon spheres (Ru/NCS) <i>via</i> pyrolysis of the polymer precursor of NCS containing Ru ions. Experimental results indicate that the interaction between Ru species and N-doped carbon leads to the formation of ultrafine RuN_<i>x</i> clusters with uniform distribution on NCS and also optimizes the Ru-H/Ru-OH bond strength, thereby promoting the rate-determining Volmer step in alkaline HER. Furthermore, the open porous structure of the NCS support is beneficial for the transport of gaseous products. Consequently, the as-synthesized Ru/NCS exhibits excellent HER performance with an overpotential of 4 mV, a low Tafel slope of 26 mV dec^-1, a high mass activity of 6.24 A mg Ru^-1 at an overpotential of 50 mV, and long-term stability over 1000 h at 10 mA cm^-2 with negligible voltage increase, outperforming state-of-the-art commercial Pt/C and Ru/C benchmarks.