Size-Controlled Boron-Based Bifunctional Photocathodes for High-Efficiency Photo-Assisted Li-O 2 Batteries.

Photo-assisted Li-O 2 batteries are introduced as a promising strategy for reducing severe overpotential by directly employing photocathodes. Herein, a series of size-controlled single-element boron photocatalysts are prepared by the meticulous liquid phase thinning methods by combining probe and water bath sonication, and their bifunctional photocathodes in the photo-assisted Li-O 2 batteries are systematically investigated. The boron-based Li-O 2 batteries have shown incremental round-trip efficiencies as the sized reduction of boron under illumination. It is noteworthy that the completely amorphous boron nanosheets (B 4 ) photocathode not only delivers an optimizing round-trip efficiency of 190% on the basis of the ultra-high discharge voltage (3.55 V) and ultra-low charge voltage (1.87 V) but also gives a high rate performance and ultralong durability with a round-trip efficiency of 133% after 100 cycles (200 h) compared with the other-sized boron photocathodes. This remarkable photoelectric performance of the B 4 sample can be attracted to the synergistic effect on the suitable semiconductor property, high conductivity, and strengthened catalytic ability of boron nanosheets coated with ultrathin amorphous boron-oxides overlayer. This research can open a new avenue to facilitate the rapid development of high-efficiency photo-assisted Li-O 2 batteries.