The need of sustainable energy sources and converter systems that combine efficiency and reduction of environmental footprint attract increasing interest. This is due to the increasing energy demand over the world (currently of ca. 2 tep per year per inhabitant), which increases the irreversible consumption of the fossil fuels, diseases related to pollutants emissions (NO_x, CO) and greenhouse effect (CO₂). In this context, fuel cells composed of systems capable of converting directly chemical energy into electrical energy, are receiving special attention mainly due to their ability to generate efficiently electricity and heat.

Hydrogen is considered as the ideal energy carrier, which can decrease the carbon footprint. It has an energy density (ca. 33000 Wh kg^-1) three times higher than that of gasoline, and during its combustion in a fuel cell, the sole reaction product is water that can be decomposed by electrolysis to obtain again hydrogen and oxygen. Therefore, its utilization in energy conversion (fuel cell) and its production from electrolysis (energy storage) will be addressed during this lecture. Proton exchange membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs) composed of platinum group metals (PGMs) are now available on the market. But the scarcity of the PGMs requires the development of electrode materials based on earth-abundant transition metals, which is line, for example, with the European roadmap for hydrogen.¹

Other molecules such as alcohols and carbohydrates are used as fuels to fabricate autonomous devices that provide low power densities. As an example, the case of glucose is of great interest for cogeneration because the electrochemical process leads to highly functionalized organic molecules into electricity, heat and value-added chemicals. It is furthermore the deliverable form of energy in living organisms and its electrooxidation in physiological media is therefore of upmost importance for numerous medical applications.

This lecture will focus on the synthesis of suitable nanomaterials towards each fuel conversion. Various physical characterizations of the prepared materials and their electrochemical analysis permitted to optimize the activity of the electrodes according to their elemental composition and structure. The construction and the electrochemical performances of the direct alcohol fuel cells will be addressed. Complementary analytical techniques were employed to quantify the reaction processes involved in each compartment and to identify the reaction products resulted from the organics combustion.

Reference:

1. https://www.fch.europa.eu/sites/default/files/documents/hlg_vision_report_en.pdf

Acknowledgements: This work was mainly conducted within the framework of a PhD thesis financially supported by the French National Research Agency (ANR) through ChemBio-Energy, E-air and IMABIC programs. K.B. Kokoh also thanks EDF Company for its financial support.