Wide Range pH-Tolerable Silicon@Pyrite Cobalt Dichalcogenide Microwire Array Photoelectrodes for Solar Hydrogen Evolution

Abstract

This study employed silicon@cobalt dichalcogenide microwires (MWs) as wide range pH-tolerable photocathode material for solar water splitting. Silicon microwire arrays were fabricated through lithography and dry etching technologies. Si@Co(OH)2 MWs were utilized as precursors to synthesize Si@CoX2 (X = S or Se) photocathodes. Si@CoS2 and Si@CoSe2 MWs were subsequently prepared by thermal sulfidation and hydrothermal selenization reaction of Si@Co(OH)2, respectively. The CoX2 outer shell served as cocatalyst to accelerate the kinetics of photogenerated electrons from the underlying Si MWs and reduce the recombination. Moreover, the CoX2 layer completely deposited on the Si surface functioned as a passivation layer by decreasing the oxide formation on Si MWs during solar hydrogen evolution. Si@CoS2 photocathode showed a photocurrent density of -3.22 mA cm(-2) at 0 V (vs RHE) in 0.5 M sulfuric acid electrolyte, and Si@CoSe2 MWs revealed moderate photocurrent density of -2.55 mA cm(-2). However, Si@CoSe2 presented high charge transfer efficiency in neutral and alkaline electrolytes. Continuous chronoamperometry in acid, neutral, and alkaline solutions was conducted at 0 V (vs RHE) to evaluate the photoelectrochemical durability of Si@CoX2 MWs. Si@CoS2 electrode showed no photoresponse after the chronoamperometry test because it was etched through the electrolyte. By contrast, the photocurrent density of Si@CoSe2 MWs gradually increased to -5 mA cm(-2) after chronoamperometry characterization owing to the amorphous structure generation.

Metal Chalcogenides on Silicon Photocathodes for Efficient Water Splitting: A Mini Overview

“…CoS 2 was not stable in alkaline solution, but CoSe 2 was stable for 50 min. However, both were stable under acidic condition, especially CoS 2 was stable for 9 h [96]. Improved photocurrent of 9 mAcm −2 at 0 V vs. RHE with onset potential of 0.18 V were obtained from CoSe 2 /p-Si MW which was prepared in the identical method with CoS 2 .…”

“…Summary of the literature papers on the heterostructures of Si/TM(D)Cs for application in PEC water splitting (WS). Analyzed from Refs [53,[68][69][70]74,75,77,78,[81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100]…”

Conformal and continuous deposition of bifunctional cobalt phosphide layers on p-silicon nanowire arrays for improved solar hydrogen evolution

“…However, the prohibitive cost and scarcity of Pt are the major limiting factors for large-scale applications of this efficient catalyst. In this context, many research works have recently focused on non-precious transition metal based HER catalysts including chalcogenides [8][9][10][11][12][13][14][15], phosphides [16][17][18][19][20][21][22][23][24], carbides [25][26][27], borides [28,29] and nitrides [30], and HER performance favorably comparable to that of Pt was already reported.…”

“…Besides, the photocurrent density at 0 V vs RHE (J0) of SiNW@Co2P-X photocathodes is substantially enhanced, amounting to -7.4, -21.9 and -12.2 mA cm -2 for SiNW@Co2P-2.25, SiNW@Co2P-4.5 and SiNW@Co2P-9, respectively. Among all samples investigated, SiNW@Co2P-4.5 is the best-performing one: it is not only better than the SiNW@Pt control sample, which has Uonset of +0.21 V vs RHE and J0 of -14.4 mA cm -2 , but also outperforms many Si-based photocathodes reported previously in the literature (Table S1) such as MoOxSy decorated SiMW arrays (Uonset = +0.24 V and J0 = -9.83 mA cm SiNWs (Uonset = +0.3 V and J0 = -15 mA cm -2 ) [12], W2C modified SiNWs (Uonset = +0.2 V and J0 = -16 mA cm -2 ) [27], and SiMW@cobalt dichalcogenide (Uonset = +0.29 V and J 0 = -3.22 mA cm -2 ) [14]. SiNW@Co2P photocathodes prepared with precursor concentrations higher than 9 mM were also tested (Figure S4), J0 and the limiting photocurrent densities of these photocathodes are found to decrease as the precursor concentration increases.…”

Enhancing solar hydrogen production with cobalt dichalcogenides

“…4 However, we found the marcasite In response to this issue, we developed thin films of CoS 2 and CoSe 2 with a pyrite structure (cubic crystal system), which act as both cocatalysts and protective passivation layers on the silicon microwire electrodes: see Figure 2(b). 5,6 The silicon microwire arrays coated with pyrite CoS 2 -and CoSe 2 were prepared through chemical deposition of cobalt(II) hydroxide, followed by thermal sulfidation or hydrothermal selenization, respectively (see Figure 3). The photocurrent density of the pyrite CoS 2 -modified silicon microwire photocathodes (with a CoS 2 film thickness of 250nm) was optimized to 3.22mAcm 2 at 0V versus a RHE, in 0.5M sulfuric acid electrolyte solution.…”