Graphene and graphene-cellulose nanocrystal composite films for sustainable anodes in biophotovoltaic devices

The urgent need for renewable energy technologies has fuelled the exploration of biophotovoltaic devices (BPVs) that harness photosynthetic microorganisms, such as cyanobacteria, for solar-to-electricity conversion. To address the need for sustainable and scalable BPV power generation, the development of suitable electrode materials is crucial. In this study, we investigated electrically conducting few-layer graphene films and composites of graphene and cellulose nanocrystals (CNC) as potential BPVs anodes. Graphene and graphene-CNC electrodes were fabricated using a green liquid-phase shear exfoliation method in aqueous environments, employing sodium cholate (SC) surfactant solution or a CNC suspension, respectively, followed by spray-coating onto non-conductive glass substrates. Both CNC and SC are non-toxic, naturally derived, and renewable. Surface characterisation revealed hydrophilic films with nanoscale roughness, ideal for interfacing cyanobacterial cells. Cyclic voltammetry experiments demonstrated the electroactivity and stability of the electrodes in aqueous electrolyte solutions compatible with cyanobacteria. The photoelectrochemical performance of cyanobacterial cells on these electrodes was evaluated using a three-electrode electrochemical set-up. The graphene and graphene-CNC electrodes harvested photocharge densities over a 5 min period of 86.0 +/- 32.0 mu C cm-2 and 52.8 +/- 23.2 mu C cm-2, respectively; and with ferricyanide 339 +/- 139 mu C cm-2 and 134 +/- 79 mu C cm-2, respectively (photocurrent densities with ferricyanide of 2.17 +/- 0.74 mu A cm-2 and 1.11 +/- 0.60 mu A cm-2, respectively). Due to their abundant source materials and efficient fabrication method, few-layer graphene and graphene-CNC composites present a sustainable solution as anodes for renewable electricity generation in BPVs. This research provides a foundation for the advancement of cost-effective and environmentally friendly BPV technologies, thereby contributing to the reduction of fossil fuel dependence in energy generation. This work demonstrates the innovative utilisation of sheer exfoliated few-layer graphene and graphene-CNC films as eco-friendly electrodes for efficient current extraction from cyanobacteria, promising advancements in biophotovoltaic applications.