Metals and metallic composites as emerging nanocatalysts for fermentative hydrogen production

Since the development of nanostructured materials, there has been a wide range of interest in their applications including improvement in microbial metabolic processes to enhance biohydrogen production. The successful application of nanostructured materials such as zerovalent metals, metal oxides and ions, and organic and inorganic composites as catalysts for lab-scale fermentative hydrogen production has been reported. Based on bibliometric analysis, nanoparticle-assisted dark fermentative hydrogen production (DFHP) has received growing attention from researchers. The present review is intended to highlight the recent development of various metals and metallic composites explored as catalysts for increased biohydrogen productivity as the end goal. The fundamental physiology of DFHP is discussed, followed by the nanoparticle-assisted DFHP. It critically addresses the significance of zerovalent metallic nanoparticles, metal-oxide nanoparticles, composite nanoparticles, and carbon-supported nanoparticles applied for dark fermentative hydrogen production. Later, the prospects of nanoparticle-bacteria interaction, integration of nanotechnology with immobilization, and genetic engineering in relation to improved hydrogen productivity are discussed with suggestions for further improvements. The interdependence of physiochemical properties and catalytic characteristics of nanoparticles provides an exciting opportunity based on the core element present at the active site of hydrogenases and promotes DFHP. Thus, such development of NPs with multi-enzymatic potential offers an immense scope for the economical scale-up of fermentative hydrogen production using a wide range of organic waste as a reality.