Graphene-based metal oxide nanocomposites for hydrogen storage in PEM fuel cell applications: a critical review

Abstract

Abstract The fast decarbonization process demands hydrogen storage technologies that are compact, safe and can easily be combined with the proton exchange membrane fuel cells. In the current paper, a critical appraisal of graphene-based nanocomposites as solid-state electrochemical hydrogen storage in low-carbon operating conditions is provided. It gives emphasis on the synthesis of graphene materials by traditional and green methods, such as plant-extract assisted reduction method and reports on its structure–property-performance correlations. Special focus is made on graphene-based metal oxides, metal-decorated systems including ZnAl₂O₄–TiO₂ composites and N-doped Pd-graphene hybrids, which have been shown to exhibit high electrochemical hydrogen storage characteristics in alkaline electrolytes at near-ambient temperatures (25°C–30°C) during galvanostatic charge discharge cycling. Reversible hydrogen storage capacity of up to an important of 7.6 wt% is of critical interest in terms of the testing conditions, cycling stability and as being dominated by electrochemical proton insertion and spillover-assisted chemisorption, as opposed to being dominated by physisorption-driven uptake [1–4]. This review has summarized evidence on more than 100 recent experimental studies to identify fundamental material design levers such as defect engineering, heteroatom doping, catalytic metal decoration, and porosity control as controlling the kinetics, reversibility and cycling durability of hydrogen uptake at low pressures and moderate electrochemical potentials. The review also indicates the significance of scalable and environmentally friendly synthesis strategies in developing a viable deployment. All in all, the article places graphene-based materials as versatile platforms to ambient-condition electrochemical hydrogen storage, and specifies the outstanding challenges and future research directions.