Rechargeable Photoactive Zn‐Air Batteries Using NiCo₂S₄ as an Efficient Bifunctional Photocatalyst towards OER/ORR at the Cathode

Abstract

Using free solar energy in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts to enhance the efficiency of zinc‐air batteries (ZABs) has not yet been widely investigated. Herein, we report a photoactive bifunctional catalyst of spinel‐type NiCo2S4 (NCS) urchin‐like structure with rich mesopores and direct band gap energies of ca. 1.4 and 2.4 eV. The NCS catalyst exhibits high catalytic activities for both OER (ɳ=338 mV at 10 mA cm−2) and ORR (ɳ=475 mV at E1/2), comparable to that of the state‐of‐the‐art counterparts (e. g., Pt/C for ORR, RuO2 for OER). Under light illumination, the p‐type photoactive NCS catalyst can absorb visible light, generating photogenerated holes and photoelectrons via the photoelectric effect for direct conversion of photoenergy into electric energy with increasing kinetics charge transfer process and provides ca. 10 and 18.5 % lower OER and ORR overpotentials, respectively than those under the dark condition. In addition, the as‐fabricated zinc‐air battery with the photoactive NCS as the cathode exhibits decrease in voltage gap from 0.82 to 0.60 V with an increasing round‐trip efficiency from 59.2 % to 68.8 % after exposed to visible light. The zinc‐air battery with a reversible redox reaction for the simultaneous conversion of chemical and photoenergy into electric energy could open a new pathway for the utilization of a single energy conversion and storage device.

Inexpensive and Abundant Layered Co-Based Composite Photocatalysts for Hydrogen Production and Theoretical Calculations

“…The band gaps of ZCS, 10CS/ZCS, and CS were 2.25, 2.1, and 1.3 eV, respectively, as shown in Figure c. The reduced band gap of the composite sample facilitated the production of photogenerated electrons under visible light excitation, which was conducive to the occurrence of the photocatalytic hydrogen production reaction …”

“…The reduced band gap of the composite sample facilitated the production of photogenerated electrons under visible light excitation, which was conducive to the occurrence of the photocatalytic hydrogen production reaction. 36 The separation of photogenerated electrons and holes is the most important step in determining the photocatalytic reaction. The transient photocurrent and impedance usually reflect the photogenerated electron concentration and the electron transfer process, and the fluorescence spectrum reflects the compound of photogenerated electrons and holes.…”

Photoelectrochemical energy storage materials: design principles and functional devices towards direct solar to electrochemical energy storage

“…In addition, metal sulfides and metal phosphides can also be used as photoelectrodes for photoassisted rechargeable ZABs, including NiCo 2 S 4 , and Ni 12 P 5 @NCNT. 117,118 For example, photoassisted ZABs with NiCo 2 S 4 photoelectrodes exhibit stable cycling performance with charge and discharge potential plateaus of ∼1.92 V and ∼1.32 V at a current density of 2 mA cm −2 under light illumination, increasing the energy efficiency from 59.2% to 68.8%. 117 Furthermore, when Ni 12 P 5 @NCNT was introduced into the ZAB, the charge/discharge voltage and energy efficiency under light were also improved due to the good photocatalytic activity of the dual functional Ni 12 P 5 @NCNT air cathode (Fig.…”

Photo‐assisted Rechargeable Metal Batteries for Energy Conversion and Storage

“…It is demonstrated that choosing semiconductor with more negative CB positions, appropriate VB positions, and high photoelectrochemical stability is effective to address the high over potential issue of zinc–air battery. Besides, metal sulfides, metal oxides, metal phosphides, and their composites can be also used as photoelectode in photo‐assisted rechargeable zinc–air battery, including NiCo 2 S 4 , [ 90 ] Co 3 O 4 , [ 91 ] CdS/TiO 2 , [ 92 ] ZnS/CdSe/CdS/TiO 2 , [ 93 ] TiO 2 /carbon papers, [ 94 ] and Ni 12 P 5 @NCNT. [ 95 ] For example, the photo‐assisted zinc–air battery with NiCo 2 S 4 photoelectode presents a stable cycling performance with the charge and discharge potential plateaus of ~1.92 V and ~1.32 V at a current density of 2 mA cm −2 under light illumination, increasing the energy efficiency from 59.2% to 68.8%.…”