Selective surface deposition of trace amount of ruthenium onto a freestanding, fibrous carbon monolith for pH-universal hydrogen evolution reaction

Among various hydrogen evolution reaction (HER) catalysts, ruthenium (Ru)-based catalysts exhibit excellent pH-universal activity, whereas the presence of inaccessible active sites buried in dense layers inevitably leads to excessive use of Ru.In addition, intentional formation of Ru nanoparticles in addition to single atoms to optimize HER activity further increases the Ru mass loading. In this study, the direct deposition of trace amount of Ru onto pre-assembled fibrous carbon monolith leads to highly efficient pH-universal HER activity with only 0.32 wt% of ultralow Ru content. The selective deposition of Ru onto only accessible active sites in three-dimensional carbon monolith suppresses the formation of buried active sites. Despite the low content, the selective deposition pathway to only accessible sites result in the formation of Ru nanoparticles, which synergize with coexisting single atoms to optimize pH-universal HER activity. The presence of Co single atoms in the fibrous carbon matrix further optimizes the deposition and HER activity of Ru species. The prepared monolithic catalyst exhibits highly efficient pH-universal HER activity with the drastically low overpotential values of 14/15/54 mV and the Tafel plots of 19/17/46 mV dec(-1) in 1 M KOH alkaline, 0.5 M H2SO4 acidic, and 1 M PBS neutral electrolytes, respectively. It also exhibits a high durability during 10,000 cycles under an accelerated reaction conditions. Differentiated from conventional powdered catalysts that typically require a ruthenium content of similar to 20%, this study suggests a novel strategy for simultaneously improving the HER activity of the catalytic electrode and reducing the use of Ru.