Laser Promoting Oxygen Vacancies Generation in Alloy via Mo for HMF Electrochemical Oxidation

Abstract It is well known that nickel‐based catalysts have high electrocatalytic activity for the 5‐hydroxymethylfurfural oxidation reaction (HMFOR), and NiOOH is the main active component. However, the price of nickel and the catalyst's lifetime still need to be solved. In this work, NiOOH containing oxygen vacancies is formed on the surface of Ni alloy by UV laser (1J85‐laser). X‐ray absorption fine structure (XAFS) analyses indicate an interaction between Mo and Ni, which affects the coordination environment of Ni with oxygen. The chemical valence of Ni is between 0 and 2, indicating the generation of oxygen vacancies. Density functional theory (DFT) suggests that Mo can increase the defect energy and form more oxygen vacancies. In situ Raman electrochemical spectroscopy shows that Mo can promote the formation of NiOOH, thus enhancing the HMFOR activity. The 1J85‐laser electrode shows a longer electrocatalytic lifetime than Ni‐laser. After 15 cycles, the conversion of HMF is 95.92%.


Density functional theory (DFT)
We have employed the Vienna Ab initio Simulation Package (VASP) to perform all density functional theory (DFT) calculations.The projector represented the elemental core and valence electrons augmented wave (PAW) method and plane-wave basis functions with a cutoff energy of 450 eV.Generalized gradient approximation with the Perdew-Burke-Ernzerh of (GGA-PBE) exchange-correlation functional was employed in all the calculations.Geometry optimizations were performed with the force convergency smaller than 0.05 eV/Å.Mo-NiO (200) is one Mo atom doping the Ni atoms on the NiO (200) surface.Monkhorst-Pack k-points of 2×2×1 were applied for all the calculations.Half atoms at the bottom are fixed in all the calculations.We used the following equations to calculate the vacancy formation energy in that order.
Here, E(Ov) was the total energy of the vacancy surface.E(O2) was the energy of O2.
Esurf was the surface energy.

X-ray absorption fine structure (XAFS) analysis
Ni and Mo K-edge analysis were performed with Si (111) crystal monochromators at the BL14W1 beamlines at the Shanghai Synchrotron Radiation Facility (SSRF) (Shanghai, China).Before the analysis at the beamline, samples were pressed into thin sheets with 1 cm in diameter and sealed using Kapton tape film.The XAFS spectra         The OER overpotential corresponding to Figure S7b.

were recorded at room temperature using a 4 -
channel Silicon Drift Detector (SDD) Bruker 5040.Ni and Mo K-edge extended X-ray absorption fine structure (EXAFS) spectra were recorded in transmission mode).Negligible changes in the line-shape and peak position of Ni and Mo K-edge XANES spectra were observed between two scans taken for a specific sample.The XAFS spectra of these standard samples (Ni foil, NiO, Ni2O3, NiPc, Mo foil, MoO2 and MoO3) were recorded in transmission mode.The spectra were processed and analyzed by the software codes Athena and Artemis.

Figure S1 .
Figure S1.(a, b) SEM images of 1J85 plate.(c-i) SEM images of the 1J85-laser surfaces prepared at laser currents of 31 to 39 A.

Figure S5 .
Figure S5.(a-d) Fitting curves of FT-EXAFS spectra corresponding to Figure 3b and Figure 3d.(b-e) k space fitting results.(c-f) q space fitting results.

Figure S6 .
Figure S6.Wavelet transform of the Ni K-edge for (a) Ni foil and (b) Mo foil.

Figure S9 .
Figure S9.With scan rates from 20 to 120 mV s -1 , the CV curves of electrodes of (a) 1J85-laser prepared by 31 A, (b) 33 A, (c) 35 A, (d) 37 A, (e) 39 A, (f) 1J85 plate, (g) Ni-laser.(h) The corresponding capacitive current at 0.15 V as a function of the scan rate for all electrodes.

Figure S10 .
Figure S10.(a) LSV curves of electrodes to HER in 1.0 M KOH.(b) Tafel slopes corresponding to (a).(c) Nyquist plots of electrodes to HER.

Figure S12 .
Figure S12.The i-t curves of 1J85-laser (a) and Ni-laser (b) at a constant potential of 1.55 V (vs.RHE) in 1.0 M KOH with 50 mM HMF.

Figure S14 .
Figure S14.HPLC curves of the products obtained by electrocatalysis with 1J85-laser (a) and Ni-laser (b).

Figure S15 .
Figure S15.(a) The oxidation path of HMF with 1J85-laser.(b-d) Estimation of rate constants for each step.

Figure S16 .
Figure S16.The i-t curves of 1J85-laser at 1.55 V with the intermittent addition of 50 mM HMF.

Figure S17 .
Figure S17.Faradaic efficiency of FDCA in five successive cycles with 1J85-laser and Ni-laser.

Figure S21 .
Figure S21.(a) With scan rates from 20 to 120 mV s -1 , the CV curves of 1J85-laser after HMFOR.(b) The corresponding capacitive current at 0.15 V as a function of the scan rate.

Figure S23 .
Figure S23.Photos of the anode 1J85-laser electrode, cathode graphite electrode and serpentine flow path.

Figure S25 .
Figure S25.Electrochemical in-situ Raman spectra of 1J36-laser (a) and 1J50-laser (b) at different potentials in 1.0 M KOH with 50 mM HMF.

Table S1 .
Structural parameters extracted from EXAFS fitting.

Table S2 .
Comparison HMFOR performance of 1J85-laser with other electrocatalysts reported in the paper under alkaline conditions.

Table S3 .
The atomic percentage of elements in 1J85-laser by TEM.