Aqueous photovoltaic technologies to drive electrochemical nitrogen reduction

The electrochemical nitrogen reduction reaction (eNRR) must be driven by renewable energy in order to be fully sustainable. Among photovoltaics, third and fourth generations are emerging as complementary to traditional silicon-based cells. These technologies are based on abundant and cheap raw materials and aim to reduce the manufacturing costs of traditional photovoltaics. In particular, dye-sensitized cells (DSSCs) offer the possibility of converting also diffuse light. Currently, DSSCs with record efficiencies are based on organic volatile electrolytes, that threat the stability and the safety of the devices during operation. Water has been proposed as non-toxic, safe and environmentally friendly solvents for electrolytes, but the performances of aqueous DSSCs are still unsatisfactory. To further decrease solvent evaporation and leakage from the device, (quasi)solid state electrolytes must be used. The gelification of a liquid electrolyte by using a polymer able to entrap the liquid phase could be a suitable strategy to obtain a (quasi)solid state electrolyte with properties similar to the liquid counterpart. Another strategy is the swelling of a polymeric membrane in the liquid electrolyte as well. In this view, cell components must be adapted to aqueous electrolyte and the interfacial contacts must be optimized. In a recent work, we added some molecular or polymeric additives to the commercial TiO2 paste, used to fabricate photoanodes by doctor blade technique. In same case, the modification of morphology and thickness of the sensitized photoanode could ameliorate the performance of the cell by 48% and 23%, in the case of liquid and gelified electrolyte, respectively. The use of waste-derived components is a suitable way to obtain sustainable electrolytes. In another work, we employed a modified lignin in the electrolyte. Lignin is an abundant material and it is produced as waste in the paper-industry, as a byproduct of the delignification of lignocellulose. Herein, we introduced some chemical transformation in the structure and swelled the membrane in the aqueous electrolyte, to obtain a stable and sustainable DSSC. The field of aqueous photovoltaic can be further developed to be coupled with eNRR.