Electronic structure optimizing of Ru nanoclusters via Co single atom and N, S co-doped reduced graphene oxide for accelerating water electrolysis.

The development of efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is impending for the advancement of water-splitting. In this study, we developed a novel electrocatalyst consisting of highly dispersed Ru nanoclusters ameliorated by cobalt single atoms and N, S co-doped reduced graphene oxide (CoSARuNC@NSG). Benefitted from the optimized electronic structure of the Ru nanoclusters induced by the adjacent single atomic Co and N, S co-doped RGO support, the electrocatalyst exhibits exceptional HER performance with overpotentials of 15 mV and 74 mV for achieving a current density of 10 mA cm-2 in alkaline and acidic water. The catalyst outperforms most noble metal-based HER electrocatalysts. Furthermore, the electrolyzer assembled with CoSARuNC@NSG and RuO2 demonstrated an overall voltage of 1.56 V at 10 mA cm-2 and an excellent operational stability for over 25 h with almost no attenuation. Theoretical calculations also deduce its high HER activity demonstrated by the smaller reaction energy barrier due to the optimized electronic structure of Ru nanoclusters. This strategy involving the regulation of metal nanoparticles activity through flexible single atom and GO support could provide valuable insights into the design of high-performance and low-cost HER catalysts.

Study on the effect of the size irregularity gradient of metal foams on macroscopic compressive properties.

Size irregularity gradient and cell wall gradient, combined as the density gradient in previous studies, affect the macroscopic mechanical properties of the gradient metal foam. More and more complex mesostructures are designed and applied in metal foams, and the density gradient becomes insufficient to describe the difference in mesostructures. To explore the effect of mesostructures carefully, this study focuses on the effect of the size irregularity gradient on the macroscopic compressive properties of metal foams. A series of metal foam models were developed using the 3D Voronoi technique. These models have the same average relative densities, the same average diameters and different size irregularity gradients. Simulation results indicated that the macroscopic mechanical properties of cell wall gradient metal foams are significantly different from those of size irregularity gradient metal foams, though these models have the same relative density gradient. To explore the effect of size irregularity gradient, a theoretical model was developed to characterize the compression process from the first cell-collapse to full condensation. Theoretical results showed a linear relationship between the nominal stress and the current relative density. These findings can provide efficient guidance for the design and applications of gradient metal foams.