Incorporation of Sulfate Anions and Sulfur Vacancies in ZnIn₂S₄ Photoanode for Enhanced Photoelectrochemical Water Splitting

Abstract

friendly properties. [6] However, due to its severe bulk carrier recombination, unfavorable carrier transportation, and sluggish surface OER dynamics, the PEC performance of bare ZnIn 2 S 4 photoanode is still not satisfactory.Various strategies have been developed to enhance the PEC performance of ZnIn 2 S 4 , such as morphology engineering, constructing heterojunctions, and coating surface co-catalysts, etc. [7][8][9] Among them, decorating surface cocatalysts has been considered as an effective strategy to promote surface water oxidation kinetics of pristine ZnIn 2 S 4 . However, the integration of water-oxidation cocatalysts with PEC photoanodes has been limited to metal-based materials, such Co-Pi, FeCoO x , and FeOOH. [10][11][12][13][14][15] The cocatalysts containing metallic ions tend to be toxic and expensive, which could limit their further applications. In addition, these cocatalysts may cause light absorption attenuation and increased charge recombination due to the large thickness/dimension of cocatalysts and additional interface defects between cocatalysts and photo anodes. Recently, nonmetallic anionic groups, such as phosphate (PO 4 3− ), selenate (SeO 4 2− ), and sulfate (SO 4 2− ), have emerged as alternatives to boost water oxidation ability. [16][17][18] These nonmetallic groups could optimize the electronic structure of active sites, regulate the adsorption of intermediates to reduce OER overpotential, and promote the surface carrier transfer. Particularly, the SO 4 2− group can break the adsorption-energy scaling relation between OH* and OOH* (reaction intermediates) and decrease the OER overpotential. [17] Accordingly, engineering ZnIn 2 S 4 with SO 4 2− groups is a promising strategy to improve its surface reaction kinetics. However, the introduction of nonmetallic anionic groups usually relies on a direct mixing method or external addition, which leads to weak chemical interaction and thus decreases the effectiveness and durability of the resultant materials. [17] In contrast, in situ introducing SO 4 2− anionic groups into ZnIn 2 S 4 to induce strong bonding between anions and metal atoms is expected to remarkably facilitate solar water oxidation.As a kind of intrinsic defect for metal sulfide, sulfur vacancies (S v ) have the ability to adjust the electronic structure of metal sulfide, leading to optimization of the adsorption free energy and also improvement of the conductivity. [19,20] S v can be divided into bulk S v and surface S v according to their spatial Severe charge recombination and slow surface water oxidation kinetics seriously limit the practical application of ZnIn 2 S 4 photoanodes for photo electrochemical water splitting. Herein, an in situ strategy to introduce sulfate (SO 4 2− ) anions and controlled bulk sulfur vacancies (S v ) into a ZnIn 2 S 4 photoanode is developed, and its PEC performance is remarkably enhanced, achieving a photocurrent density of 3.52 mA cm −2 at 1.23 V versus reversible hydrogen electrode (V RHE ) and negatively shifted onset potential of 0....

Engineering Interfacial Band Bending over ZnIn2S4/SnS2 by Interface Chemical Bond for Efficient Solar‐Driven Photoelectrochemical Water Splitting

“…A new characteristic peak in both ZIS-TS and ZIS-O-TS appears at 15.0° indexed to the (001) crystal facet of hexagonal TS (JCPDS: 23-0677), which proves the heterojunction formation. Raman spectra indicate distinct photon modes at 242 and 349 cm −1 , consistent with the vibrational modes of ZIS, [29] and the peak intensities at 128 and 303 cm −1 also become stronger as the degree of oxidation increases, indicating the existence of InO bonds (Figure 1g; Figure S6a, Supporting Information). [30] Meanwhile, the peak at 306 cm −1 corresponds to a characterized mode of TS and becomes more obvious as the time of loading TS extends (Figure S6b, Supporting Information).…”

Recent research progress on operational stability of metal oxide/sulfide photoanodes in photoelectrochemical cells

“…With the in-depth study of photoanodes by researchers, the performance of photoanodes has improved substantially [7]. Many processing strategies, such as heteroatom doping, cocatalyst loading, heterostructure construction, crystal face control, vacancy introduction, and interface engineering, have been applied to modify photoanodes [8][9][10][11]. The performance of photoanodes has improved rapidly in recent years.…”

Heterostructure-Induced Light Absorption and Charge-Transfer Optimization of a TiO2 Photoanode for Photoelectrochemical Water Splitting

“…The intensity of the PL peak is related to the recombination chance between an electron and a hole. 43 As shown in Figure 4e, the intensity of the PL peak shows a significant decrease after incorporating NiTiO 3 onto TiO 2 NRAs, which strongly evidences that the NiTiO 3 /TiO 2 heterojunction can effectively suppress recombination of the photogenerated electrons and holes. Furthermore, the TRPL was measured to reveal the dynamics of the photogenerated charge carriers.…”

“…To further understand the separation, migration, and transfer of photogenerated charge carriers, the PL spectra were recorded. The intensity of the PL peak is related to the recombination chance between an electron and a hole . As shown in Figure e, the intensity of the PL peak shows a significant decrease after incorporating NiTiO 3 onto TiO 2 NRAs, which strongly evidences that the NiTiO 3 /TiO 2 heterojunction can effectively suppress recombination of the photogenerated electrons and holes.…”