A 3D-printed freestanding graphene aerogel composite photocathode for high-capacity and long-life photo-assisted Li-O2 batteries

The construction of a high-performance photocathode is essential for improving Li-O-2 battery performance and solar energy utilization. However, the single pore and few active reaction sites of the photocathode result in insufficient discharge capacity and unsatisfactory cycling durability. Herein, we designed and fabricated a self-standing 3D-printed multi-pore graphene-based photocathode via direct ink writing (DIW) featuring non-competitive three-phase transmission channels to promote the transport of Li+, e(-), and O-2. The macropore provides adequate space for storage of the Li2O2 discharge product; the mesopore facilitates the reactant transport, while the micropore stores the active ions. Furthermore, the photogenerated carriers of the photocathode promote overpotential reduction. Under illumination, the charging voltage of the Li-O-2 battery with a reduced graphene oxide/titanium dioxide (rGO/TiO2) photocathode is decreased from 4.55 V to 3.77 V, and the battery exhibits stable cycling for 1000 hours. Notably, the photocathode's pore structure and specific surface area are further optimized after adding carbon nanotubes (CNTs). Compared with rGO/TiO2, the specific surface area of reduced graphene oxide/titanium dioxide/carbon nanotubes (rGO/TiO2/CNTs) is increased by 12 times to 194.13 m(2) g(-1), and the discharge capacity can reach up to 33.37 mA h cm(-2). This self-standing 3D-printed photocathode structure paves a new way for developing high-performance energy storage systems.