Optimized Metal Chalcogenides for Boosting Water Splitting

Abstract

Electrocatalytic water splitting (2H₂O → 2H₂ + O₂) is a very promising avenue to effectively and environmentally friendly produce highly pure hydrogen (H₂) and oxygen (O₂) at a large scale. Different materials have been developed to enhance the efficiency for water splitting. Among them, chalcogenides with unique atomic arrangement and high electronic transport show interesting catalytic properties in various electrochemical reactions, such as the hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting, while the control of their morphology and structure is of vital importance to their catalytic performance. Herein, the general synthetic methods are summarized to prepare metal chalcogenides and different strategies are designed to improve their catalytic performance for water splitting. The remaining challenges in the research and development of metal chalcogenides and possible directions for future research are also summarized.

Keywords: electronic structure; enhanced catalysis; metal chalcogenides; synthetic methods; water splitting.

Scheme 1

The metal chalcogenides applied in water splitting.

Scheme 2

The mechanism of HER in a) acid and b) alkaline media (b). The mechanism of OER in c) acid and d) alkaline media.

Figure 1

Illustration of typical synthesis and application of metal chalcogenides.

Figure 2

The principal methods for synthesizing metal chalcogenides.

Figure 3

a−d) FESEM images and e−h) TEM images of the as‐synthesized products obtained at different time intervals: 1 h a,e), 6 h b,f), 12 h c,g), and 20 h d,h). i−l) Schematic illustration of the formation process of Ni−Co−MoS₂ nanoboxes. Reproduced with permission.129 Copyright 2016, John Wiley‐VCH.

Figure 4

a) TEM and b) HRTEM micrograph of Pt icosahedra with an edge length of 8.8 nm. Reproduced with permission.211 Copyright 2013, American Chemical Society. c) Schematic illustration of hot‐injection methods and TRM for the obtained products. Reproduced with permission.212 Copyright 2016, American Chemical Society.

Figure 5

a–c) TEM image, size distribution, and HRTEM image of circular Cu₂S nanocrystals. d–f) TEM image, size distribution, and HRTEM image of elongated Cu₂S nanocrystals. g–i) TEM image, size distribution, and HRTEM image of Cu₂S hexagonal nanoplates. Reproduced with permission.215 Copyright 2008, American Chemical Society. Schematics of the particle geometries at top panel in right. SEM images of self‐assembled superlattices of hexagonal bipyramid‐shaped ZnS NCs A) and hexagonal bifrustum‐shaped ZnS NCs B). Snapshots of 2D self‐assembly of hexagonal bipyramids C,D,F,G) and hexagonal bifrustums E,H) adhered to an air−toluene interface. Reproduced with permission.216 Copyright 2014, American Chemical Society.

Figure 6

A–I) Formation of various Cu_1.8S based nanostructures with different morphology through cathode exchange method. Cu, Cd, and Zn are shown in red, blue, and green in TEM images and STEM‐EDS elements maps. J) Crystal structure projections of wurtzite CdS, roxbyite Cu_1.8S, and wurtzite ZnS, which highlight the crystallographic relationships between the adjacent phases and intraparticle frameworks. K) EDS spectra of selected regions for all samples. The Ni signal is from the Ni TEM grid. Reproduced with permission.193 Copyright 2018, AAAS.

Figure 7

a–c) HAADF‐STEM, BF‐STEM images, and atomic‐resolution HAADF‐STEM image of CdS/CdTe heterodimer. d) Z‐contrast profile of anion/cation pair columns in the blue rectangular region in (c). e,f) Magnified images of the yellow and red rectangular regions for e) CdS and f) CdTe phases in (c), respectively. Scale bars = 1 nm. g) Illustration of the CdS/CdTe heterointerface. Reproduced with permission.228 Copyright 2011, American Chemical Society.

Figure 8

A) Schematic illustration of a modified CVD system for the robust epitaxial growth of lateral heterostructures. The solid powders were directly used as the source material. The obtained various 2D nanocrystals monolayer seed (A,B), A‐B heterostructure (C), A‐B‐C multiheterostructure (D), and A‐B‐A‐B superlattice (E). Reproduced with permission.237 Copyright 2017, AAAS.

Figure 9

a) HRTEM and b) EDX‐STEM elemental mapping images, c) Atomic‐resolution aberration‐corrected HAADF‐STEM image, and d) the corresponding model of the Cu_1.94S−Zn_0.23Cd_0.77S heterointerface. Reproduced with permission.117 Copyright 2016, American Chemical Society.

Figure 10

a) TEM, b) HRTEM, c) HAADF‐STEM images, and d) corresponding FFT image of HAADF‐STEM for Co‐NiS₂ NSs. e) Crystal structure of Co‐NiS₂ NSs depicting Ni/Co cations as blue spheres and S in orange; Surface intensity and atomic columns simulated by using QSTEM software along f,g) [101] and h,i) [100] zone axes. Reproduced with permission.250 Copyright 2019, Wiley‐VCH.

Figure 11

a–d) SEM and TEM images for CoS and 14.6 % CeOx/CoS. e,f) The HRTEM images and corresponding SAED pattern (the inset in (f)) of 14.6 % CeO_x/CoS. g) Elemental mapping images of 14.6 % CeO_x/CoS. Reproduced with permission.251 Copyright 2018, Wiley‐VCH.

Figure 12

A) Schematic illustration for fabricating thick orthorhombic phase CoSe₂ sheets. B) SAXS profile (red line and inset left image), XRD pattern (blue line) and the corresponding lateral TEM image for the lamellar hybrid CoSe₂‐DETA intermediate. C) HRTEM image of the thick orthorhombic phase CoSe₂ sheets. D) AFM image and E) the corresponding height profiles for the thick orthorhombic phase CoSe₂ sheets. Reproduced with permission.254 Copyright 2015, Wiley‐VCH.

Figure 13

A,B) Photos, C) XRD pattern, and D−F) top‐view SEM images of the Ni₃S₂/NF. Inset in (E): side‐view SEM image of Ni₃S₂/NF. G) HRTEM image of the Ni₃S₂/NF, with the fast Fourier transform image shown in the inset. Reproduced with permission.67 Copyright 2015, American Chemical Society.

Figure 14

a) Illustration of synthesized process of A‐CoS_4.6O_0.6 PNCs. b) SEM image of Co‐Fe PBA precursor. c,d) SEM images at different magnification. e–g) TEM, HRTEM image, and SAED pattern of A‐CoS_4.6O_0.6 PNCs. Reproduced with permission.120 Copyright 2017, Wiley‐VCH.

Figure 15

a–e) Schematic illustration of the preparation of mesoporous 1T phase MoS₂ nanosheets from bulk MoS₂. Reproduced with permission.56 Copyright 2016, American Chemical Society.

Figure 16

a,d) Schematic illustration of home‐built APCVD setup and WS₂/MoS₂ in‐plane heterojunctions. b,c,e) Optical, AFM and SEM image of the WS₂/MoS₂ in‐plane heterojunctions. Reproduced with permission.177 Copyright 2015, Wiley‐VCH.