Oxidation Reaction Process Research Articles

Photoelectrochemical Ethylene Glycol Oxidization Coupled with Hydrogen Generation Using Metal Oxide Photoelectrodes.

Photoelectrochemical (PEC) water splitting represents a promising approach for harnessing solar energy and transforming it into storable hydrogen. However, the complicated 4-electron transfer process of water oxidation reaction imposes kinetic limitations on the overall efficiency. Herein, we proposed a strategy by substituting water oxidation with the oxidation of ethylene glycol (EG), which is a hydrolysis byproduct of polyethylene terephthalate (PET) plastic waste. To achieve this, we developed and synthesized BiVO4/NiCo-LDH photoanodes capable of achieving a high Faradaic efficiency (FE) exceeding 85 % for the oxidation of EG to formate in a strongly alkaline environment. The reaction mechanism was further elucidated using in situ FTIR spectroscopy. Additionally, we successfully constructed an unassisted PEC device for EG oxidation and hydrogen generation by pairing the translucent Mo : BiVO4/NiCo-LDH photoanode with a state-of-the-art Cu2O photocathode, resulting in an approximate photocurrent density of 2.3 mA/cm2. Our research not only offers a PEC pathway for converting PET plastics into valuable chemicals but also enables simultaneous hydrogen production.

Photoelectrochemical Ethylene Glycol Oxidization Coupled with Hydrogen Generation Using Metal Oxide Photoelectrodes

AbstractPhotoelectrochemical (PEC) water splitting represents a promising approach for harnessing solar energy and transforming it into storable hydrogen. However, the complicated 4‐electron transfer process of water oxidation reaction imposes kinetic limitations on the overall efficiency. Herein, we proposed a strategy by substituting water oxidation with the oxidation of ethylene glycol (EG), which is a hydrolysis byproduct of polyethylene terephthalate (PET) plastic waste. To achieve this, we developed and synthesized BiVO4/NiCo‐LDH photoanodes capable of achieving a high Faradaic efficiency (FE) exceeding 85 % for the oxidation of EG to formate in a strongly alkaline environment. The reaction mechanism was further elucidated using in situ FTIR spectroscopy. Additionally, we successfully constructed an unassisted PEC device for EG oxidation and hydrogen generation by pairing the translucent Mo : BiVO4/NiCo‐LDH photoanode with a state‐of‐the‐art Cu2O photocathode, resulting in an approximate photocurrent density of 2.3 mA/cm2. Our research not only offers a PEC pathway for converting PET plastics into valuable chemicals but also enables simultaneous hydrogen production.

Metal Organic Frameworks‐Derived NiO/NiCo2O4 Heterostructures for Effective Methanol Oxidation Reaction

AbstractThe electrochemical process of methanol oxidation reaction (MOR), which is closely associated with electrochemical production of formate and hydrogen, is considered a highly viable avenue for advancing renewable energy technologies. Nevertheless, the development and creation of affordable, effective, and durable electrocatalysts for MOR continue to present significant obstacles. In this study, a hierarchical porous NiO/NiCo2O4/NF electrode is fabricated through the integration of solvothermal and thermal oxidation treatments of Ni‐MOF‐74 and NiCo‐Asp. After thoroughly assessing the electrochemical performance for MOR, NiO/NiCo2O4/NF demonstrates a significant current density of 140 mA cm−2 at 1.6 V (vs. RHE) and a tafel slop of 45.0 mV·dec−1 in 1 M KOH and 0.5 M methanol. The excellent performance of MOR can be ascribed to the hierarchical porous nature that enhances mass and electron transport while offering numerous active sites for electrocatalytic reactions. Additionally, the hetero interface between NiO and NiCo2O4 could further enhance electron transfer rate and reaction kinetics for the MOR. The developed NiO/NiCo2O4/NF electrode shows potential as a viable and economical alternative to Pt‐based electrocatalysts for MOR‐based applications.

Investigating the kinetics, thermodynamic properties, and mechanisms of high-temperature oxidation in ferrosilicon alloys

Ferrosilicon alloys are widely used as a deoxidizer in steelmaking due to their strong oxygen affinity and high deoxidizing ability. However, compared to other deoxidizers, relatively few studies have been conducted on its kinetics, thermodynamics, and reaction mechanisms. This study aims to investigate the oxidation characteristics of ferrosilicon alloys at different particle sizes, reaction temperatures, and reaction times, and to evaluate their oxidation structure and reaction characteristics. To achieve this, we used the response surface methodology (RSM) to establish a multi-factor model. The results show that reaction time and reaction temperature are the primary factors affecting the oxidation rates, followed by particle size. Wagner’s law was used to verify that the change in oxidation mass follows the parabolic rate law and was discussed in relation to other alloys. Additionally, the application of the volumetric model (VM) and the unreacted core model (URCM) in calculating the activation energy (E) was compared to understand the kinetic characteristics of ferrosilicon alloys more comprehensively. Specifically, when the particle size range increases from 0.075–––0.1 mm to 0.3–––0.5 mm, the estimated E of the VM model increases from 81.82 KJ·mol−1 to 87.84 KJ·mol−1. The URCM model’s result increases from 91.53 KJ·mol−1 to 97.21 KJ·mol−1. Additionally, we evaluated the thermodynamic feasibility of ferrosilicon alloys at temperatures ranging from 273.15 K to 1673.15 K using HSC Chemistry software. This paper describes in detail the oxide layer structure and oxidation reaction process of ferrosilicon alloys and proposes an oxidation reaction mechanism, providing a reliable theoretical basis for the application system of ferrosilicon alloys.

Synchrotron vacuum ultraviolet photoionization mass spectrometry and modeling study of iso-octane low temperature oxidation at varied pressures

Because of its excellent anti-knock properties, iso-octane has been selected as the main component of gasoline surrogates, and a thorough understanding of its low temperature oxidation process is essential for the development of kinetic models. Although iso-octane has been studied for decades, a comprehensive understanding of its low temperature oxidation chemistry has not been realized, and kinetic models were not well developed. In this work, the previously developed, variable pressure jet-stirred reactor-synchrotron vacuum ultraviolet photoionization mass spectrometry system was used to study the low temperature oxidation of iso-octane at five bar, with an initial fuel mole fraction of 0.01, residence time of 2 s, and equivalence ratio of 0.25. Dozens of oxidation intermediates were qualitatively and quantitatively analyzed, helping to reveal the low temperature oxidation reaction processes of iso-octane and examine the kinetic models. Comparing iso-octane studies at high pressure in the literature, a highly detailed species pool was probed, which included H2O2, carbonyl acids, alkyl hydroperoxides, and keto-hydroperoxides (KHP). By combining the atmospheric pressure data in the literature, the recently developed model of iso-octane low temperature oxidation was examined. Further improvement of the kinetic model was achieved by carefully tuning the reaction rate constant of the KHP decomposition. Finally, according to the variation of mole fraction of products at different pressures, the pressure effects on key reaction pathways were discussed, and the selectivity of products at varied pressure conditions clarified.

Bottle-in-bottle reaction device: Portable gas pressure meter for rapid and on-site analysis of oxalate in spinach and tea beverages

A gas pressure meter-based portable/miniaturized analytical kit was established for rapid and on-site detection of oxalate. Potassium permanganate (KMnO4) and oxalate solution were mixed together in bottle-in-bottle reaction device, a simple oxidation reaction process occurred within 6 min and carbon dioxide (CO2) was generated, inducing the pressure of the sealed bottle changed, which was measured by a portable gas pressure meter. A detectable range of 0.1–6 μmol mL−1 and a detection limit of 0.064 μmol mL−1 were achieved. The proposed analytical method was further used for the analysis of several real samples (spinach, beverages and water samples), with the recoveries of 89–111%. Considering the interferences from the complicated matrix, calcium chloride (CaCl2) was served as a precipitant, oxalate (C2O42−) was precipitated with Ca2+ to form precipitation (CaC2O4), CaC2O4 was then separated from the matrix by centrifuge/filter, eliminating the interferences. It is a rapid, easy-used and interference-free analytical system/device for oxalate on-site and real time analysis.

Tensile Strain and Interatomic Orbital Hybridization Effects Boost the Electrocatalytic Performance of Intermetallic Pd3Pb Nanowires for Ethanol Electrooxidation†

Comprehensive SummaryWe present a strategy that effectively modulate the d‐band electronic structure of the active center by strain effect and interatomic orbital hybridization. This strategy efficiently promotes the kinetic process of the ethanol oxidation reaction (EOR) in alkaline media. In the intermetallic Pd3Pb nanowires, the introduction of Pb not only causes the lattice expansion of Pd but also achieves the interatomic orbital hybridization bonding with Pd. Such interatomic orbital hybridization effect and tensile strain effect can effectively achieve a co‐regulation of the d‐band electronic structure of Pd, which directly affects the adsorption behavior of intermediate on Pd for EOR. Hence, the intermetallic Pd3Pb nanowires demonstrate enhanced EOR activity and anti‐poisoning ability against COads. Theoretical calculations show that the enhanced OH* adsorption ability and the low energy barrier for the oxidative dehydrogenation of ethanol are the keys to high EOR activity and stability of the intermetallic Pd3Pb nanowires.

Revealing operando surface defect–dependent electrocatalytic performance of Pt at the subparticle level

Understanding the operando defect-tuning performance of catalysts is critical to establish an accurate structure-activity relationship of a catalyst. Here, with the tool of single-molecule super-resolution fluorescence microscopy, by imaging intermediate CO formation/oxidation during the methanol oxidation reaction process on individual defective Pt nanotubes, we reveal that the fresh Pt ends with more defects are more active and anti-CO poisoning than fresh center areas with less defects, while such difference could be reversed after catalysis-induced step-by-step creation of more defects on the Pt surface. Further experimental results reveal an operando volcano relationship between the catalytic performance (activity and anti-CO ability) and the fine-tuned defect density. Systematic DFT calculations indicate that such an operando volcano relationship could be attributed to the defect-dependent transition state free energy and the accelerated surface reconstructing of defects or Pt-atom moving driven by the adsorption of the CO intermediate. These insights deepen our understanding to the operando defect-driven catalysis at single-molecule and subparticle level, which is able to help the design of highly efficient defect-based catalysts.

The role of Au and Pd in photocatalytic activation of molecular oxygen: A mechanistic study

Activation of molecular oxygen plays an important role in photocatalytic selective oxidation reactions and complete degradation of organic pollutants. Noble metal cocatalysts are often employed to modulate the activation of oxygen to reach an optimum photocatalytic performance. However, the role of the metal nanoparticles (NPs) still remains unclear and deserves investigation for the design of efficient photocatalysts. Here, Au and Pd NPs are deposited on the TiO2 photocatalyst to study the promotional mechanism of O2 dissociation with the presence of glycerol under irradiation by near-ambient-pressure photoelectron spectroscopy and in-situ spectrometry approaches. While both Au and Pd NPs can dissociate O2 into activated oxygen species, a relatively strong bonds of dissociated oxygen atom is observed on Au NPs than on the Pd NPs. This results in a moderate reduction rate of O2 and eventually favors a mild oxidation reaction process for Au, and a rapid reduction rate of O2 and eventually a deep oxidation reaction process for Pd, respectively.

Interface Enables Faster Surface Reconstruction in a Heterostructured CuSey/NiSex Electrocatalyst for Realizing Urea Oxidation.

Creating affordable electrocatalysts and understanding the real-time catalytic process of the urea oxidation reaction (UOR) are crucial for advancing urea-based technologies. Herein, a Cu-Ni based selenide electrocatalyst (CuSey/NiSex/NF) was created using a hydrothermal technique and selenization treatment, featuring a heterogeneous interface rich in Cu2-xSe, Cu3Se2, Ni3Se4, and NiSe2. This catalyst demonstrated outstanding urea electrooxidation performance, achieving 10 mA cm-2 with just 1.31 V and sustaining stability for 96 h. Through in-situ Raman spectroscopy and ex-situ characterizations, it is discovered that NiOOH is formed through surface reconstruction in the UOR process, with high-valence Ni serving as the key site for effective urea oxidation. Moreover, the electrochemical analysis revealed that CuSey had dual effects. An analysis of XPS and electrochemical tests revealed that electron transfer from CuSey to NiSex within the CuSey/NiSex/NF heterostructure enhanced the UOR kinetics of the catalyst. Additionally, according to the in-situ Raman spectroscopy findings, the existence of CuSey facilitates a easier and faster surface reconstruction of NiSex, leading to the creation of additional active sites for urea oxidation. More significantly, this work provides an excellent "precatalyst" for highly efficient UOR, along with an in-depth understanding of the mechanism behind the structural changes in electrocatalysts and the discovery of their true active sites.

High-precision identification of polarization processes of proton exchange membrane fuel cells through relaxation time analysis: Targeted experimental design and verification

Distribution of relaxation time (DRT) technology can achieve more precise decoupling of polarization process of proton exchange membrane fuel cell (PEMFC). However, except for the two peaks of DRT at low frequency, which are widely acknowledged to the cathode charge transfer impedance and the oxygen mass transfer impedance, there has been ongoing debate regarding the interpretation of other peaks observed at high frequency. In this work, the single-state variable control method is introduced by design of the membrane electrode assembly (MEA) and corresponding working operating conditions to simulate performance degradation factors of PEMFC, enabling accurate identification and verification of each peak in DRT. Based on the previous understanding that peaks P1 and P2 are oxygen mass transfer impedance and cathode charge transfer impedance, peaks P3-P5, ranging from high to low time scales, are determined to correspond to the other three polarization impedances. Specifically, peaks P3 and P4 are influenced by ionomer content in cathode and anode catalyst layers, respectively, and exhibit a decline with increasing humidity. They correspond to proton transfer processes within their respective catalyst layers. And the peak P5 is affected by anode catalyst loading and displays an increase with rising current density at low loading, signifying its involvement in the charge transfer process of anodic hydrogen oxidation reaction. A novel ECM was developed, consisting of five series-connected Randles circuits with polarization significance. The cathode and anode were separated in this design. The results demonstrate the enhanced sensitivity of DRT analysis to the performance degradation of PEMFC caused by oxygen transfer, charge transfer, and proton migration. This perspective provides a clear refinement for prior work of DRT polarization characteristic peaks.

Electrochemical Properties of NiCo2O4/WO3/Activated Carbon Wheat Husk Nano-Electrocatalyst for Methanol and Ethanol Oxidation

It is common to use efficient catalysts in the anodes and cathodes of methanol and ethanol fuel cells, such as platinum and ruthenium. However, due to their expansivity and rarity, finding a suitable alternative is important. In this work, multi-component catalysts consisting of tungsten oxide, nickel cobaltite, and activated carbon were synthesized through the hydrothermal method. The performance of catalysts in the processes of methanol and ethanol oxidation reactions (MOR and EOR) were investigated. The addition of activated carbon obtained from wheat husk, with an excellent active surface and acceptable electrical conductivity, to the matrix of the catalyst significantly facilitated the oxidation process of alcohols and enhanced the efficiency of the catalyst. The physical and electrochemical characterization of the NiCo2O4/WO3 hybridized with the wheat husk-derived activated carbon (ACWH) catalyst indicated its successful synthesis and good performance in the alcohol oxidation process. NiCo2O4/WO3/ACWH with an oxidation current density of 63.39 mA/cm2 at the peak potential of 0.58 V (1.59 vs. RHE), a cyclic stability of 98.6% in the methanol oxidation reaction (MOR) and 27.98 mA/cm2 at the peak potential of 0.67 V (1.68 vs. RHE), and a cyclic stability of 95.7% in the ethanol oxidation reaction (EOR) process can be an interesting option for application in the anodes of alcohol fuel cells.

Kornblum Oxidation Reaction-Induced Collective Transformation of Lead Polyhalides for Stable Perovskite Photovoltaics.

The iodide vacancy defects generated during the perovskite crystallization process are a common issue that limits the efficiency and stability of perovskite solar cells (PSCs). Although excessive ionic iodides have been used to compensate for these vacancies, they are not effective in reducing defects through modulating the perovskite crystallization. Moreover, these iodide ions present in the perovskite films can act as interstitial defects, which are detrimental to the stability of the perovskite. Here, an effective approach to suppress the formation of vacancy defects by manipulating the coordination chemistry of lead polyhalides during perovskite crystallization is demonstrated. To achieve this suppression, an α-iodo ketone is introduced to undergo a process of Kornblum oxidation reaction that releases halide ions. This process induces a rapid collective transformation of lead polyhalides during the nucleation process and significantly reduces iodide vacancy defects. As a result, the ion mobility is decreased by one order of magnitude in perovskite film and the PSC achieves significantly improved thermal stability, maintaining 82% of its initial power conversion efficiency at 85°C for 2800h. These findings highlight the potential of halide ions released by the Kornblum oxidation reaction, which can be widely used for achieving high-performance perovskite optoelectronics.

Carbon Quantum Dots Confined into Covalent Triazine Frameworks for Efficient Overall Photocatalytic H2O2 Production

AbstractPorous organic polymers have an outstanding performance in the field of photocatalysis with the advantage of diverse structure composition and purposeful molecular design. However, the inherent high impedance and poor electrical conductivity of organic semiconductors still restrict the charge transfer efficiency and thus discount the photocatalytic performance. Herein, the study reports a highly conductive covalent triazine framework (CTF) loading carbon quantum dots (CQDs) into porous as electron transport medium. The addition of CQDs (0.5 wt%) can enhance the electronic conductivity of CTF by tenfold. In addition, the as‐prepared CQD‐CTFs express much‐promoted charge separation and transfer efficiency. Furthermore, the embedded CQDs can improve the oxidization capacity and increase the affinity of H+ due to the more negative zeta potential. The enhanced oxidizing ability and increased H+ affinity are positive for water oxidation reaction (WOR) and oxygen reduction reaction (ORR) process in hydrogen peroxide (H2O2) generation, respectively. The optimized CQD‐CTF exhibits a high H2O2 generation rate of up to 1036 µmol g−1 h−1 in pure water without any sacrificial agent under visible light, which is 4.6 times than pristine CTF. This work provides a new idea for efficient H2O2 production of organic semiconductors.

Porous hemispherical Au@PdAg catalysts for enhancing ethanol electrooxidation

Direct ethanol fuel cell can convert chemical energy into electric energy directly, and has the advantages of being free from Carnot cycle and being friendly to environment, so it has a broad application prospect. However, the insufficient activity and toxicity resistance of anodic catalysts limit their commercial application, mainly due to the limited adsorption sites and the toxic inactivation of catalysts resulting from the production of toxic intermediates (COads) during the ethanol oxidation reaction (EOR) process. In this study, the Au@PdAg porous hemispherical catalyst assembled by nanotubes was successfully prepared by soft template method and co-reduction method using dioctadecyl dimethyl ammonium chloride (DODAC) as surfactant, and its EOR performance was tested. Au@Pd1.0Ag1.0 has the highest mass current density with a peak value of 4048.8 mAmgPd−1, which is 7.8 times of Pd/C (JM). After 5000 s stability test, the residual current density value is still 863.4 mAmgPd−1. The results showed that the introduction of the oxygenophilic metal Ag was conducive to the formation of OHads and the oxidation of COads. The porous structure of the nanotube assembly facilitates electron transfer and provides more adsorption sites, which makes the catalyst show good electrocatalytic activity and anti-CO poisoning ability.

Single Atom Catalyst in Persulfate Oxidation Reaction: From Atom Species to Substance.

With maximum utilization of active metal sites, more and more researchers have reported using single atom catalysts (SACs) to activate persulfate (PS) for organic pollutants removal. In SACs, single metal atoms (Fe, Co, Cu, Mn, etc.) and different substrates (porous carbon, biochar, graphene oxide, carbon nitride, MOF, MoS2, and others) are the basic structural. Metal single atoms, substances, and connected chemical bonds all have a great influence on the electronic structures that directly affect the activation process of PS and degradation efficiency to organic pollutants. However, there are few relevant reviews about the interaction between metal single atoms and substances during PS activation process. In this review, the SACs with different metal species and substrates are summarized to investigate the metal-support interaction and evaluate their effects on PS oxidation reaction process. Furthermore, how metal atoms and substrates affect the reactive species and degradation pathways are also discussed. Finally, the challenges and prospects of SACs in PS-AOPs are proposed.

CuNi2O4/MWCNTs nanocatalyst for methanol and ethanol electro-oxidation

The widespread use of cheap and efficient catalysts in energy storage and production in electrochemical processes led our research team to the synthesis and evaluation of CuNi2O4/MWCNTs nanocatalyst for alcohol oxidation. Nanocatalyst was characterized in terms of structure and morphology by X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDAX). The ability of CuNi2O4/MWCNTs was evaluated with cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses in the oxidation process of methanol and ethanol alcohols in alkaline media. The optimal concentration of methanol and ethanol for CuNi2O4/MWCNTs and CuNi2O4 was obtained to investigate the methanol oxidation reaction and ethanol oxidation reaction processes. The mechanism of these processes was also evaluated in detail. The stability of both nanocatalysts was investigated by performing several consecutive CVs and in 3600 s by chronoamperometric analysis. The results showed the good stability of this catalyst. The synergistic effect of placing CuNi2O4 on the surface of carbon nanotubes improved the oxidation process of methanol and ethanol. In general, the proposed catalyst can be an efficient, stable, and cheap option and at the same time very stable for use in alcohol fuel cells.

Tuning Redox Behavior of Sulfur Cathodes Via Ternary-Coordinated Single Fe Atom in Lithium-Sulfur Batteries.

Modulating the coordination configuration of single Fe atom has been an efficient strategy to strengthen the redox dynamics for lithium-sulfur batteries (LSBs) but remains challenging. Herein, the single Fe atom is functioned with nitrogen and carbon atoms in the first shell, and simultaneously, oxidized sulfur (─SOx) in the second shell, which presents a lower antibonding state and well address the redox activity of sulfur cathodes. In the ternary-coordinated single Fe atom catalyst (FeN2C2-SOx-NC), the binary structure of FeN2C2 provides a lower Fe-S bonding strength and d-p orbital hybridization, which obviously optimizes the adsorption and desorption behavior of sulfur species during the reduction and oxidation reaction processes. Simultaneously, the ─SOx redistributes the electron density of the coordinating nitrogen atoms, which possesses high electron-withdrawing ability and develops electrocatalytic activity. As a result, the sulfur cathodes with FeN2C2-SOx-NC present an excellent high-rate cyclic performance, accompanied by a capacity decay rate of 0.08% per cycle for 500 cycles at 4.0 C. This study provides new insights for optimizing the redox dynamics of sulfur cathodes in LSBs at the atomic level.

Low-temperature oxidative removal of benzene from the air using titanium carbide (MXene)-Supported platinum catalysts

MXenes are an emerging class of two-dimensional (2D) inorganic materials with great potential for versatile applications such as adsorption and catalysis. Here, we describe the synthesis of a platinized titanium carbide MXene (Pt@Ti3C2) catalyst with varying amounts of platinum (0.1%–2 wt.%) for the low-temperature oxidation of benzene, an aromatic volatile organic compound often found in industrial flue gas. A 1% formulation of Pt@Ti3C2–R allowed near-complete (97%) oxidation of benzene to CO2 at 225 °C with a steady-state reaction rate (r) of 0.119 mol g−1·h−1. This low-temperature catalytic oxidation reaction was promoted by an increase in the lattice oxygen (O*)/Pt2+ species (active sites) of 1%Pt@Ti3C2–R from 45.3/34.6% to 71.0/61.1% through pre-thermal reduction under H2 flow, as revealed by X-ray photoelectron spectroscopy, temperature-programmed reduction, and in situ diffuse reflectance infrared Fourier transform spectroscopy analyses. The cataltyic activity of 1% Pt@Ti3C2–R against benzene was assessed under the control of the key process variables (e.g., catalyst mass, flow rate, benzene concentration, relative humidity, and time-on-stream) to help optimize the oxidation reaction process. The results provide new insights into the use of platinum-based 2D MXene catalysts for low-temperature oxidative removal of benzene from the air.

Unveiling the mechanism of electrocatalytic oxidation of glycerol by in-situ electrochemical spectroscopy

The electrocatalytic glycerol oxidation reaction (GOR) is an efficient way to reduce the overpotential of the anodic reaction of electrocatalytic water splitting with abundant high-value byproducts. However, it has always been difficult to reveal a clear reaction path and real active site during the electrocatalytic glycerol oxidation reaction (GOR) process. In this work, NiOOH/Ni3S2/NF, a model catalyst was synthesized by the two-step method, and the reaction path of the electrocatalytic oxidation of glycerol on NiOOH/Ni3S2/NF was clearly unveiled by the in situ infrared and Raman analysis. In addition, the TEM after GOR and in-situ Raman intuitively demonstrated that the NiOOH was the real active site during the GOR process. Consequently, the synthesized NiOOH/Ni3S2/NF catalyst achieved a current density of 10 mA cm−2 at 1.227 V vs. RHE and obtained a high formic acid Faraday efficiency of 97.7 % at a low potential of 1.4 V vs. RHE. This work demonstrates an effective method for unveiling the GOR mechanism and the other relevant electrocatalytic reaction processes.