Applications of Lignin in Energy Conversion: Solar Cells, Fuel Cells and Photocatalysis

As the need to produce more sustainably and fight climate change is becoming a primordial and urgent research interest, energy conversion, which consists in transforming some renewable energy source like light or biomass to electricity or chemical energy, has attracted a lot of attention. Indeed, the different processes involving energy conversion could provide some interesting solutions in the effort to be less dependent on fossil fuel and to consider the environmental impact. Nanomaterials and nanocomposites derived from lignin have found more and more applications in energy-conversion processes and devices. As a cheap and abundant biopolymer, lignin and its derivatives could offer greener alternatives to some of the materials currently used. This chapter will focus on three different aspects of energy conversion: solar cells, fuels cells, and photocatalysis. In photovoltaic devices, lignin nanomaterials have been employed as absorber, electrolyte, in the preparation of electrodes or hole-transporting materials. In fuel cells, lignin could directly act as fuel to produce electricity, but it could also help improving the properties of membranes and electrodes through incorporation of its nanoderivatives. In photocatalysis, nanolignin, and other nanomaterials prepared from it, have essentially been used as support for the metallic catalysts.