A 2.4 V Aqueous Zinc-Ion Battery Enabled by the Photoelectrochemical Effect of a Modified BiOI Photocathode: Shattering the Shackle of the Electrochemical Window of an Aqueous Electrolyte

Abstract

Aqueous zinc-ion batteries emerge as a promising energy storage system with merits of high security, abundance, and being environmentally benign. But the low operating voltages of aqueous electrolytes restrict their energy densities. Previous reports have mostly focused on modifying the electrolytes to enlarge the operating voltages of aqueous zinc-ion batteries. However, either extra-expensive salts or potential safety hazards of organic additives are considered to be adverse for practical large-scale applications. Here, a proof-of-concept to enlarge the operating voltage of an aqueous zinc-ion battery by incorporating a well-designed semiconductor photocathode is proposed, which produces a photovoltage (V ph ) across the semiconductor/liquid junction (SCLJ) interface to elevate the output voltage of zinc-ion battery under irradiation. The operating voltage of an aqueous zinc-ion battery can be markedly raised from 1.78 (thermodynamic limit) to 2.4 V when a BiOI nanoflake array photocathode with good surface modification is introduced, achieving a round-trip efficiency of 114.3% and a 34.8% increase of energy density compared to the theoretical value. The successive ionic layer adsorption and reaction modified surface effectively passivates surface trap defects of the BiOI photocathode and thus enlarges its V ph from 60 to 240 mV under irradiation. This study provides a design to enlarge the output voltages of aqueous zinc-ion batteries and other energy storage systems, providing insight into widening the voltage window, which is that the operating voltages are determined by photocathode under irradiation and not restricted by the electrochemical stability window of dilute aqueous electrolytes.

Boosting Energy Storage in Metal Batteries by Light: Progress, Challenges, and Perspectives

“…Copyright 2019 Wiley-VCH. Panels c–e were reprinted from ref . Copyright 2024 American Chemical Society.…”

“…However, the trap defects existing on the surface of the BiOI photocathode generally act as recombination centers of photoexcited carriers, leading to the V ph being far from the theoretical value. Thus, we introduced a surface modification layer to passivate the surface trap defects of the BiOI photocathode, inhibiting surface recombination of photoexcited carriers and thus enlarging V ph upon light illumination (Figure c,d), the resulting aqueous Zn-ion battery demonstrated an operation potential of 2.4 V (Figure e). This work provides an additional option to extend the electrochemical window of conventional aqueous electrolytes rather than tuning the composition of the aqueous electrolytes.…”

“…Copyright 2022 American Chemical Society. Panel d was reprinted with permission from ref . Copyright 2024 American Chemical Society.…”