Bio-fuel cells are alternative energy devises based on bio-electrocatalysis of natural substrates by enzymes or microorganisms. Here we review bio-fuel cells and bio-batteries based on the recent literature. In general, the bio-fuel cells are classified based on the type of electron transfer; mediated electron transfer and direct electron transfer or electronic charge transfer (ECT). The ECT of the bio-fuel cells is critically reviewed and a variety of possible applications are considered. The technical challenges of the bio-fuel cells, like bioelectrocatalysis, immobilization of bioelectrocatalysts, protein denaturation etc. are highlighted and future research directions are discussed leveraging on the use of electron charge transfer proteins. In addition, the packaging aspects of the bio-fuel cells are also analyzed and the found that relatively little work has been done in the engineering development of bio-fuel cells.

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Nanostructured components are introduced in membrane electrodes assembly ͑MEA͒ in proton exchange membrane fuel cell as a solution to improve the performance. Single-walled carbon nanotubes and multiwalled carbon nanotubes supported platinum are used to fabricate the gas diffusion layer ͑GDL͒ and the catalyst layers in the MEAs, respectively. The physicochemical and electrochemical characterizations of these nanotube-based components demonstrate excellent GDL surface morphology and uniform distribution of the platinum catalyst over the carbon nanotube support. The fuel cell testing using these nanostructured components exhibits promising fuel cell performance using hydrogen-air and hydrogen-oxygen at ambient pressure.

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