MnO2-decorated highly porous 3D-printed graphene supercapacitors for photosynthetic power systems

Abstract

Harvesting of photosynthetic electrons (PEs) from photosynthetic cells or isolated photosynthetic apparatus holds great prospects for environmentally friendly energy generation. However, the low current output and power density still remain significant challenges. Here, we propose highly porous MnO₂-decorated 3D-printed graphene electrodes that enhance thylakoid adhesion, PE extraction and storage and dramatically increase areal PE current density. With optimized graphene oxide (GO) hydrogel inks composed of GO, hydroxypropyl methylcellulose (HPMC) and Carbomer 940, GO microlattices are 3D printed and thermally reduced to highly porous 3D graphene electrodes. Among different deposition methods, potentiodynamic electrodeposition of MnO₂ onto the electrode surface results in both the highest porosity and largest surface area. MnO₂ facilitates the firm adhesion of thylakoid membranes (TMs) and down-shifts the mid potential for more favorable oxidation of PE carriers in photosynthetic apparatuses. With these enhancements, a 3D MnO₂-graphene electrode achieves a 50 fold higher capacitance (304 F g⁻¹) than bare graphene electrodes. When TMs are coated, PE current density dramatically improves by 30 fold (580 μA cm⁻²) compared to PE current from bare graphene electrodes. Finally, full cell tests demonstrated light-triggered self-charging performances with an OCV of 333 mV and produced a power density of up to 930 mW m⁻².