Spillover technique for enhancement of hydrogen adsorption capacity of metal organic frameworks

Abstract

This review presents an overview of the hydrogen spillover process, a viable approach to enhance H2 adsorption capabilities of metal-organic frameworks (MOFs). Three primary strategies can increase the effectiveness of spillover namely, physical mixing, carbon bridge building, and doping. Spillover by physically mixing supported noble-metal catalyst and MOF increases the proximity between the catalyst and MOF, facilitating an effective diffusion of disassociated H atoms. However, physical mixing leads to partial destruction of the MOF structure. Spillover by carbon bridge building on the other hand, ensures intimate contact between the catalyst and MOF leading to enhanced H2 adsorption. Doping is another technique to optimize spillover by efficient dispersion of metal nanoparticles. Besides dispersion, the size of nanoparticles also plays a crucial role in spillover by doping. MOFs doped with small sized and well dispersed nanoparticles are ideal candidates for an effective spillover process. The future of spillover depends on enhancing bridge building techniques, creating smaller catalysts, and improving their dispersion on the MOF surface. A thorough study of spillover technique is critically analyzed and frameworks for further improvements are provided.