Direct alkaline alcohol fuel cells (DAAFCs) have attracted increasing interest over the past decade because of their favourable reaction kinetics in alkaline media, higher energy densities achievable and the easy handling of the liquid fuels. In this review, principles and mechanisms of DAAFCs in alcohol oxidation and oxygen reduction are discussed. Despite the high energy densities available during the oxidation of polycarbon alcohols they are difficult to oxidise. Apart from methanol, the complete oxidation of other polycarbon alcohols to CO 2 has not been achieved with current catalysts. Different types of catalysts, from conventional precious metal catalyst of Pt and Pt alloys to other lower cost Pd, Au and Ag metal catalysts are compared. Non precious metal catalysts, and lanthanum, strontium oxides and perovskite-type oxides are also discussed. Membranes like the ones used as polymer electrolytes and developed for DAAFCs are reviewed. Unlike conventional proton exchange membrane fuel cells, anion exchange membranes are used in present DAAFCs. Fuel cell performance with DAAFCs using different alcohols, catalysts and membranes, as well as operating parameters are summarised. In order to improve the power output of the DAAFCs, further developments in catalysts, membrane materials and fuel cell systems are essential. OPEN ACCESSEnergies 2010, 3 1500

Direct oxidation alkaline fuel cells (DOAFCs) possess particular advantages on the possibility of employing low cost non-noble metal catalysts. A wide range of fuels can be used due to superior reaction kinetics in alkaline media. The development of DOAFCs was hindered by the carbonation of electrolyte due to the presence of CO 2 . The application of the anion exchange membrane (AEM) provides the possibility of reducing the effect of carbonation and fuel crossover which is an issue in the proton exchange membrane fuel cells (PEMFCs). The latest developments in alkaline fuel cells are examined in this paper, considering different types of fuels, novel catalysts and anion exchange membranes. Moreover, alkaline fuel cell systems and configurations are studied, particularly the new designs for portable or microelectronic devices. Further development of DOAFCs will rely on novel AEMs with good ionic conductivity and stability, low cost non-Pt catalysts with high activity and good stability for various fuels and oxidant. We envisage that DOAFCs will play a major role in energy research and applications in the near future.

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Despite some success with microbial fuel cells and microbial electrolysis cells in recovering resources from wastes, challenges with their scale and yield need to be resolved. Waste streams from biorefineries e.g. bioethanol and biodiesel plants and wastewaters are plausible substrates for microbial electrosynthesis (MES). MES integration can help biorefineries achieving the full polygeneration potentials, i.e. recovery of metals turning apparently pollutants from biorefineries into resources, production of biofuels and chemicals from reuse of CO2 and clean water. Symbiotic integration between the two systems can attain an economic and environmental upside of the overall system. We envision that electrochemical technologies and waste biorefineries can be integrated for increased efficiency and competitiveness with stillage released from the latter process used in the former as feedstock and energy resource recovered from the former used in the latter. Such symbiotic integration can avoid loss of 2 material and energy from waste streams, thereby increasing the overall efficiency, economics and environmental performance that would serve towards delivering the common goals from both the systems. We present an insightful overview of the sources of organic wastes from biorefineries for integration with MES, anodic and cathodic substrates and biocatalysts. In addition, a generic and effective reaction and thermodynamic modelling framework for the MES has been given for the first time. The model is able to predict multi-component physico-chemical behaviour, technical feasibility and best configuration and conditions of the MES for resource recovery from waste streams.

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