Non‐Metal Sulfur Doping of Indium Hydroxide Nanocube for Selectively Photocatalytic Reduction of CO2 to CH4: A “One Stone Three Birds” Strategy

Abstract Photocatalytic CO2 reduction is considered as a promising strategy for CO2 utilization and producing renewable energy, however, it remains challenge in the improvement of photocatalytic performance for wide‐band‐gap photocatalyst with controllable product selectivity. Herein, the sulfur‐doped In(OH)3 (In(OH)xSy‐z) nanocubes are developed for selective photocatalytic reduction of CO2 to CH4 under simulated light irradiation. The CH4 yield of the optimal In(OH)xSy‐1.0 can be enhanced up to 39 times and the CH4 selectivity can be regulated as high as 80.75% compared to that of pristine In(OH)3. The substitution of sulfur atoms for hydroxyl groups in In(OH)3 enhances the visible light absorption capability, and further improves the hydrophilicity behavior, which promotes the H2O dissociation into protons (H*) and accelerates the dynamic proton‐feeding CO2 hydrogenation. In situ DRIFTs and DFT calculation confirm that the non‐metal sulfur sites significantly weaken the over‐potential of the H2O oxidation and prevent the formation of ·OH radicals, enabling the stabilization of *CHO intermediates and thus facilitating CH4 production. This work highlights the promotion effect of the non‐metal doping engineering on wide‐band‐gap photocatalysts for tailoring the product selectivity in photocatalytic CO2 reduction.

Data reduction, data analysis, and EXAFS fitting were performed and analyzed with the Athena and Artemis programs of the Demeter data analysis packages that utilizes the FEFF6 program to fit the EXAFS data. [2]The energy calibration of the sample was conducted through standard and In foil, which as a reference was simultaneously measured.A linear function was subtracted from the pre-edge region, then the edge jump was normalized using Athena software.The χ(k) data were isolated by subtracting a smooth, third-order polynomial approximating the absorption background of an isolated atom.The  5 mesoporous-In(OH)3 0.80 100 [5] 6 ZnIn2S4/In(OH)3-x 0 (Only produced CO) 0 [6] 7 Bi-doped In(OH)3 0 (Only produced CO) 0 [7] 8 ZnS-In(OH)3 7% 0 (Only produced CO) 0 [8] 9 TP/In(OH)3 0 (Only produced CO) 0 [9]

Figure S1
Figure S1 BET diagrams and pore size distribution charts (inset) of In(OH)3 and In(OH)xSy-z samples.

Figure S2
Figure S2 Possible formation mechanism of In(OH)3 and In(OH)xSy-z nanocubes.

Figure S4
Figure S4 The band-gap of In(OH)3 and In(OH)xSy-z samples.

Figure S6
Figure S6 The diagram of the electronic band structure of In(OH)3 and In(OH)xSy-z samples.

Figure S9
Figure S9 Production rate of H2 over In(OH)3 sample and In(OH)xSy-z sample.

Figure S10
Figure S10TCD signal in the gas chromatograph during the CO2 photoreduction.

Figure S11
Figure S11 The (a) XRD, (b) high resolution XPS of S 2p, (c-d) TEM images and (e-f) EDS element mapping images of the spent-In(OH)xSy-1.0 after 5 successive cycle tests.

Figure S13
Figure S13 The fs-TA kinetic decay plots and corresponding fitting curves of In(OH)3 and In(OH)xSy-1.0 at (a) 396 nm and (b) 407 nm.

Figure
Figure S14 DFT-calculated Gibbs free energy diagrams of H2O activation and dissociation on the surfaces of In(OH)3 sample.

Figure
Figure S16 Gibbs free energy diagrams of reaction pathways.Photocatalytic CO2 reduction on the surfaces of In(OH)xSy-1.0.The lilac lines refer to the pathway of CO* and CHO* formation, while the pale green lines refer to the pathway of *HCOOH and HCOOH formation.
d ΔE0, inner potential correction; R factor indicates the goodness of the fit.* This value was fixed during EXAFS fitting, based on the known structure of In.S0 2 was fixed to 0.815, according to the experimental EXAFS fit of In foil by fixing CN as the known crystallographic value.Fitting range: 2.0 ≤ k (/Å) ≤ 12.5 and 1.1 ≤ R (Å) ≤ 2.3 (In(OH)3 and

k 3 -
weighted χ(k) data were Fourier transformed after applying a HanFeng window function (Δk = 1.0).For EXAFS modeling, The global amplitude EXAFS (CN, R, σ 2 and ΔE0) were obtained by nonlinear fitting, with least-squares refinement, of the EXAFS equation to the Fourier-transformed data in Rspace, using Artemis software, EXAFS of the In foil are fitted and the obtained amplitude reduction factor S0 2 value (0.815) was set in the EXAFS analysis to determine the coordination numbers (CNs) in the In-O and In-S scattering path in sample.

Table S1
Comparison of corresponding microscopic parameters of different substances.Table S2Comparison of corresponding microscopic parameters of different samples.
b Obtained from BET method.

Table S4
Comparison of the CH4 yield and selectivity of In(OH)xSy-z with recently reported In(OH)3based photocatalysts.