Amino-group and space-confinement assisted synthesis of small and well-defined Rh nanoparticles as efficient catalysts toward ammonia borane hydrolysis

Hydrogen evolution from ammonia borane (AB) hydrolysis is of great importance considering the ever-increasing demand for green and sustainable energy. However, the development of a facile and efficient strategy to construct high-performance catalysts remains a grand challenge. Herein, we report an amino-group and space-confinement assisted strategy to fabricate Rh nanoparticles (NPs) using amino-functionalized metal-organic-frameworks (UiO-66-NH₂) as a NP matrix (Rh/UiO-66-NH₂). Owing to the coordination effect of amino-group and space-confinement of UiO-66-NH₂, small and well-distributed Rh NPs with a diameter of 3.38 nm are successfully achieved, which can be served as efficient catalysts for AB hydrolysis at room temperature. The maximum turnover frequency of 876.7 min^?1 is obtained by using the Rh/UiO-66-NH₂ with an optimal Rh loading of 4.38 wt% and AB concentration of 0.2 M at 25 °C, outperforming most of the previously developed Rh-based catalysts. The catalyst is also stable in repetitive cycles for five times. The high performance of this catalyst must be ascribed to the structural properties of UiO-66-NH₂, which enable the formation of small and well-dispersed Rh NPs with abundant accessible active sites. This study provides a simple and efficient method to significantly enhance the catalytic performance of Rh for AB hydrolysis.     

Spatially localized fabrication of uniform Rh nanoclusters on nanosheet-assembled hierarchical carbon architectures as excellent electrocatalysts for boosting alkaline hydrogen evolution

Construction of homogenously distributed and ultrafine Rh nanoclusters (NCs) anchored on suitable support with low loading toward hydrogen evolution reaction (HER) is paramount but remains challenging. Here, we developed a space confinement-assisted strategy for the construction of highly dispersed and ultrasmall Rh NCs supported on 3D nanosheet-assembled hierarchical carbon architectures (NHCAs) as advanced electrocatalysts for alkaline HER. Benefiting from the abundant and ultrasmall micro/mesopores of NHCAs, uniformly dispersed Rh NCs with diameters of 1.83 nm were embedded in NHCAs without the aid of surface capping agents. The resultant Rh NCs/NHCAs exhibited excellent electrochemical HER activity with low overpotentials of 7 and 48 mV at 10 and 100 mA cm⁻² current densities in basic solution, respectively, superior than most of the previous developed electrocatalysts. The surface-clean and ultrafine Rh NCs with high dispersity on the NHCAs surface could provide abundant surface-active sites and resulted in the high performance of Rh NCs/NHCAs for HER. The present study may offer a novel yet convenient pathway to synthesize highly dispersed and catalytically active supported noble metal electrocatalyst for catalytic applications.