Rate-determining Step Of Reaction Research Articles

Polyol-Intermediated Facile Synthesis of B5-Site-Rich Ru-Based Nanocatalysts for COx-Free Hydrogen Production via Ammonia Decomposition.

Herein, a B5-site-rich Ru/MgAl2O4 nanocatalyst for the production of COx-free hydrogen from ammonia (NH3) is synthesized using the polyol method. The polyol method enables size-sensitive Ru-nanoparticle growth and controlled B5-site formation on the catalyst by tuning the carbon-chain length of the polyol solvent used, obviating the use of a separate stabilizer and enhancing electron donation from Ru (with a high surface electron density) and π-back bonding. The Ru/MgAl2O4 (BG) catalyst synthesized using butylene glycol (a long-carbon-chain solvent) contains 2.5nm Ru particles uniformly dispersed on its surface and abundant B5 sites at (0 0 2)/(0 1 1). Moreover, the Ru/MgAl2O4 (BG) catalyst exhibits lower activation energy (48.9kJmol-1) and higher H2 formation rate (565-1,236mmol gcat -1 h-1 at 350-450°C and a weight hourly space velocity of 30,000mL gcat -1 h-1) during the NH3 decomposition reaction than catalysts with a similar Ru particle size and high metal dispersion synthesized by the impregnation and deposition-precipitation methods. This high performance is possibly because the abundant electron-donating B5 sites on the catalyst surface accelerate the recombination-desorption of N2, which is the rate-determining step of the NH3 decomposition reaction at low temperatures. Thus, this study facilitates clean hydrogen production.

Oxygen vacancy-rich Nd-doped RuO2 for efficient acid overall water splitting

The development of highly active and acid-stable Ru-based electrocatalysts is of great significance for water electrolysis but remains a huge challenge due to serious Ru corrosion in an acid medium. Herein, we prepared oxygen vacancy (OV)-rich Nd-doped RuO2 nanocrystals by facile synthesis via hydrothermal and subsequent annealing for efficient overall water splitting. The catalyst exhibits an overpotential of only 200 mV for OER and 44 mv for HER at the current density of 10 mA cm−2 in 0.5 M H2SO4 electrolyte. Nd-doped RuO2 only demands a cell voltage of 1.52 V to drive the overall water splitting reaction and displays excellent stability for 100 h. Density functional theory further revealed that the newly constructed Nd-doped RuO2 sites activate the difficult to react *O intermediates, reducing the adsorption energy of the OER intermediates to effectively minimize the Gibbs free energy (*O to *OOH) of the reaction rate-determining step and regulate the center of the active site d-band. The synergistic effect of aliovalent doping and vacancy engineering contributes to the excellent electrocatalytic performance of Nd-doped RuO2. This performance control strategy can pave the way for the development of effective and economically viable catalysts.

Atomically dispersed bimetallic FeZn-N-C with oxidase-like performance: Synthesis, characterization, calculation and activity

The burgeoning interest in single atom catalysts (SACs) stems from their exceptional oxidase-mimicking capabilities, driving substantial advancements in this field. Nevertheless, a critical knowledge gap remains regarding the influence of Zn incorporation on the oxidase-like activity of atomically dispersed Fe-N-C catalysts. This study successfully synthesized and comprehensively characterized three distinct SACs (FeZn SAC-N@C, Fe SAC-N@C, and Zn SAC-N@C) using TEM, HAADF-STEM, XRD, XPS, BET, ICP-MS, and XAFS techniques. Activity assays revealed that FeZn SAC-N@C exhibited the highest oxidase-mimicking activity, with Fe SAC-N@C displaying moderate activity, whereas Zn SAC-N@C did not exhibit oxidase-like behavior. The superior oxidase-like activity of FeZn SAC-N@C is attributed to its enhanced O2 activation capacity, characterized by a high free energy of 0.90 eV in the rate-determining reaction step, surpassing those of Fe SAC-N@C (0.85 eV) and Zn SAC-N@C (0.71 eV). EPR and DFT calculations elucidated the catalytic mechanism of FeZn SAC-N@C, involving the generation of O2− radicals. As a proof-of-concept, FeZn SAC-N@C demonstrates potential as a colorimetric sensor for detecting ascorbic acid and nitrite, achieving a limit of detection of 0.77 μM for ascorbic acid and 0.16 μM for nitrite. These findings open a new avenue for configuring bimetallic atomically dispersed catalysts with oxidase-like activity in future research.

A MOF@MOF S-scheme Heterojunction with Lewis Acid-Base Sites Synergistically Boosts Cocatalyst-Free CO2 Cycloaddition.

The photocatalytic cycloaddition reaction between CO2 and epoxide is one of the most promising green routes for CO2 utilization, for which high performance photocatalysts are intensely desired. Herein, we have constructed an S-scheme heterojunction of MIL-125@ZIF-67 modified by amino groups, which achieves a cyclic carbonate yield of as high as 99 % without employing any co-catalyst, outperforming the previously reported photocatalysts. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in-situ electron paramagnetic resonance (EPR) spectroscopy reveal the important role of photogenerated electron migration from Lewis acid (Co) sites to the O atom of epoxide in triggering its ring-opening (the rate-determining step of CO2 cycloaddition reaction) under the assistance of photogenerated hole. Synergistically and concurrently, the Lewis base (amino groups) sites activate CO2 to CO2*, facilitating the following CO2 cycloaddition. Such a synergistic effect provides a most favorable approach to design efficient heterogeneous photocatalysts with dual/multiple-active sites for CO2 cycloaddition reaction.

Double-Shell Co3O4 with Rich Surface Octahedron Oxygen Vacancies for High-Selectivity Electrocatalytic Chlorine Evolution.

The development of non-noble-metal-based chlorine evolution reaction (CER) catalysts with excellent activity, kinetics, and selectivity is urgently needed but still remains a major challenge. In this study, a morphology self-evolving and surface octahedron oxygen-vacancy-generating strategy is applied at double-shell nanospheres to obtain the target hierarchical double-shell Co3O4 nanospheres with abundant surface oxygen vacancies (DS-Co3O4-OVs). The DS-Co3O4-OVs display an overpotential of only 52 mV to reach a current density of 10 mA cm-2 in which an excellent chlorine selectivity of 98.9-99.9% is attained, which is better than that of the commercial RuO2/IrO2. Furthermore, density functional theory calculations demonstrate that the involved oxygen vacancies can not only limit the lattice oxygen mechanism of the oxygen evolution reaction process but also significantly improve the kinetics of the Volmer step to enhance the CER performance. Meanwhile, the unique hierarchical double-shell nanospheres can enhance the mass feeding and promote the rate-determining step of the Krishtalik step chlorine gas desorption reaction for enhanced kinetics. The self-evolution of non-noble catalysts with surface octahedron vacancies and the related exploration of the CER mechanism may provide a novel design idea for CER catalysts.

Function regionalized catalyst promoted bromine redox kinetics for bromine-based flow battery

Bromine-based flow batteries are considered as ideal large-scale energy storage devices, due to their attractive high energy density and low cost. However, the inferior redox activity of the Br3−/Br− couple leads to limited power density, which cannot meet the practical application requirements. Herein, a flexible catalytic electrode is constructed by interweaving a nitrogen-doped porous carbon (NPC) coated TiO2 (TiO2@NPC) nanofiber, via electrospinning technique. In the electrode, the NPC component with superior affinity to the reactant Br−, could assistant rapid charge transfer, and facilitate the conversion from Br− to Br3−, which plays an excellent catalytic function. With a stronger adsorption for the oxidation product Br3− than NPC, the TiO2 component can transfer Br3− from NPC, releasing the catalytic active sites on NPC timely and enabling the reaction smoothly proceeded. Consequently, the regional differentiation strategy of the catalysis and adsorption functions significantly boosts the redox kinetic of the bromine chemistry. The Zinc-bromine flow batteries equipped with TiO2@NPC can run 200 cycles stably at 80 mA cm−2, with the voltage efficiency and energy efficiency of 82.8 % and 81.6 %, respectively. This design provides a brand-new improvement strategy for bromine cathode from the perspective of accelerating the reaction rate-determining step.

Design of TiO2-based bi-functional catalyst and the catalytic mechanism of enhanced hydrazine borane hydrolysis for hydrogen production

In this study, a scheme of photocatalytic coupled metal catalytic synergistic enhancement of hydrazine borane hydrolysis is proposed, the catalytic reaction mechanism for hydrogen production from hydrazine borane hydrolysis is revealed. In addition, the effects of solvent property, external electric field conditions on the stability of N2H4BH3 molecule are also investigated systematacially. The results show that the band structure of pure TiO2 can be modulated by heterogeneous element N, C, Ni, Ru, the modification effect of co-doping with heterogeneous alloy elements (eg. NiPt@N–TiO2) is best in all doping schemes. The hydrolysis reaction of -BH3 of N2H4BH3 catalyzed by Pt metal is a stepwise dehydrogenation reaction, and the energy barrier of the reaction rate-determining of the B–N bond breakage is 50.49 kcal/mol. There are two possible cleavage reaction pathways for N2H4, which are hydrogen-producing pathway and ammonia-producing pathway, the energy barrier for the reaction rate-determining step is 67.06 kcal/mol and 82.51 kcal/mol, respectively, the hydrogen production reaction takes precedence over the ammonia production reaction. OH− solution is best among the neutral aqueous solution, rich H+, NH4+ and NaOH solution in B–H bond activation of N2H4BH3 molecule, the external electric field can promote the activation of B–H bond in hydrazine borane hydrolysis system, which is positive factor in improving the performance of hydrazine borane hydrolysis.

Biaxial strain induced OH engineer for accelerating alkaline hydrogen evolution

The sluggish kinetics of Volmer step in the alkaline hydrogen evolution results in large energy consumption. The challenge that has yet well resolved is to control the water adsorption and dissociation. Here, we develop biaxially strained MoSe2 three dimensional nanoshells that exhibit enhanced catalytic performance with a low overpotential of 58.2 mV at 10 mA cm−2 in base, and long-term stable activity in membrane-electrode-assembly based electrolyser at 1 A cm−2. Compared to the flat and uniaxial-strained MoSe2, we establish that the stably adsorbed OH engineer on biaxially strained MoSe2 changes the water adsorption configuration from O-down on Mo to O-horizontal on OH* via stronger hydrogen bonds. The favorable water dissociation on 3-coordinated Mo sites and hydrogen adsorption on 4-coordinated Mo sites constitute a tandem electrolysis, resulting in thermodynamically favorable hydrogen evolution. This work deepens our understanding to the impact of strain dimensions on water dissociation and inspires the design of nanostructured catalysts for accelerating the rate-determining step in multi-electron reactions.

Boron-Induced Interstitial Effects Drive Water Oxidation on Ordered Ir-B Compounds.

Interstitial filling of light atoms strongly affects the electronic structure and adsorption properties of the parent catalyst due to ligand and ensemble effects. Different from the conventional doping and surface modification, constructing ordered intermetallic structures is more promising to overcome the dissolution and reconstruction of active sites through strong interactions generated by atomic periodic arrangement, achieving joint improvement in catalytic activity and stability. However, for tightly arranged metal lattices, such as iridium (Ir), obtaining ordered filling atoms and further unveiling their interstitial effects are still limited by highly activated processes. Herein, we report a high-temperature molten salt assisted strategy to form the intermetallic Ir-B compounds (IrB1.1) with ordered filling by light boron (B) atoms. The B residing in the interstitial lattice of Ir constitutes favorable adsorption surfaces through a donor-acceptor architecture, which has an optimal free energy uphill in rate-determining step (RDS) of oxygen evolution reaction (OER), resulting in enhanced activity. Meanwhile, the strong coupling of Ir-B structural units suppresses the demetallation and reconstruction behavior of Ir, ensuring catalytic stability. Such B-induced interstitial effects endow IrB1.1 with higher OER performance than commercial IrO2, which is further validated in proton exchange membrane water electrolyzers (PEMWEs).

Accelerating the Rate-Determining Steps of Sulfur Conversion Reaction for Lithium-Sulfur Batteries Working at an Ultrawide Temperature Range.

Wide operation temperature is the crucial objective for an energy storage system that can be applied under harsh environmental conditions. For lithium-sulfur batteries, the "shuttle effect" of polysulfide intermediates will aggravate with the temperature increasing, while the reaction kinetics decreases sharply as the temperature decreasing. In particular, sulfur reaction mechanism at low temperatures seems to be quite different from that at room temperature. Here, through in situ Raman and electrochemical impedance spectroscopy studies, the newly emerged platform at cryogenic temperature corresponds to the reduction process of Li2S8 to Li2S4, which will be another rate-determining step of sulfur conversion reaction, in addition to the solid-phase conversion process of Li2S4 to Li2S2/Li2S at low temperatures. Porous bismuth vanadate (BiVO4) spheres are designed as sulfur host material, which achieve the rapid snap-transfer-catalytic process by shortening lithium-ion transport pathway and accelerating the targeted rate-determining steps. Such promoting effect greatly inhibits severe "shuttle effect" at high temperatures and simultaneously improves sulfur conversion efficiency in the cryogenic environment. The cell with the porous BiVO4 spheres as the host exhibits excellent rate capability and cycle performance under wide working temperatures.

Self-Powered Electrochemical CO2 Conversion Enabled by a Multifunctional Carbon-Based Electrocatalyst and a Rechargeable Zn-Air Battery.

Multifunctional electrocatalysts are required for diverse clean energy-related technologies (e.g., electrochemical CO2 reduction reaction (CO2RR) and metal-air batteries). Herein, a nitrogen and fluorine co-doped carbon nanotube (NFCNT) is reported to simultaneously achieve multifunctional catalytic activities for CO2RR, oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). Theoretical calculations reveal that the superior multifunctional catalytic activities of NFCNT are attributed to the synergistic effect of nitrogen and fluorine co-doping to induce charge redistribution and decrease the energy barrier of rate-determining step for different electrocatalytic reactions. Furthermore, the rechargeable Zn-air battery (ZAB) with NFCNT electrode delivers a high peak power density of 230mWcm-2 and superior durability over 100 cycles, outperforming the ZAB with Pt/C+RuO2 based electrodes. More importantly, a self-driven CO2 electrolysis unit powered by the as-assembled ZABs is developed, which achieves 80% CO Faraday efficiency and 60% total energy efficiency. This work provides a new insight into the exploration of highly efficient multifunctional carbon-based electrocatalysts for novel energy-related applications.

Electron-deficient Co7Fe3 induced by interfacial effect of molybdenum carbide boosting oxygen evolution reaction

Developing a high-activity and low-cost catalyst to reduce the anodic overpotential is essential for hydrogen production from water splitting. In this work, a hetero-structured Co7Fe3/Mo2C@C catalyst has been developed to efficiently catalyze oxygen evolution reaction (OER), the overpotential (ƞ10) of Co7Fe3/Mo2C@C-catalyzed OER with current density of 10 mA/cm2 is about 254 mV, substantially lower than the counterparts of Co7Fe3@C-catalyzed OER (ƞ10, 308 mV) and Mo2C@C-catalyzed OER (ƞ10, 439 mV), close to that of OER catalyzed by commercial RuO2. The mechanistic studies reveal that the distinct electron transfer across the Co7Fe3/Mo2C interface results in electron-deficient Co7Fe3, which has been identified as the highly active catalytic sites. Density functional theory (DFT) calculations manifest that Mo2C induces a distinct decrease in electron density on Co7Fe3 and upgrades the d-band centers of Co and Fe in Co7Fe3 towards Fermi energy level, thus substantially lowering the energy barrier of the rate-determining reaction step and conferring significantly improved OER activity on the Co7Fe3/Mo2C@C catalyst.

Elucidating reaction mechanisms in the oxidative depolymerization of sodium lignosulfonate for enhancing vanillin production: A Density Functional Theory study

Lignin is a vital organic constituent of plant biomass and it can be transformed into value-added chemicals through chemical processes. This study employs the Density Functional Theory (DFT) to investigate the mechanistic effects of various oxidants on the depolymerization of sodium lignosulfonate model compounds into vanillin. Under alkaline conditions, OH- ions participation in the hydrolysis of β-O-4 bonds has been predicted. The dehydration of dihydroconiferyl alcohol to form eugenol, with an energy barrier of 69.0 kcal/mol was identified as the major rate-determining step in the oxidation reaction. In the absence of an oxidant, the energy barrier for the oxidation of eugenol to vanillin was 77.8 kcal/mol. However, when using nitrobenzene or H2O2 as oxidants, the energy barrier has significantly decreased to 12.6 kcal/mol and 21.4 kcal/mol, respectively. The effects of temperature and pressure on the rate-determining step of the reaction were analyzed using Statistical Product and Service Solutions (SPSS) software. These results have demonstrated that the energy barrier for the hydrolysis reaction's rate-determining step is positively correlated with temperature but negatively correlated with pressure. These theoretical findings would potentially help in designing the experiments and aid in enhancing the selectivity and yield of vanillin.

Piezo-Fenton catalysis in Fe3O4-BaTiO3 nanocomposites: A low-cost and highly efficient degradation method without the additive of H2O2 or Fe(II) ions

The Fenton reaction, an effective advanced oxidation process (AOP) for degrading organic pollutants, requires the addition of H2O2 that is expensive and not environmentally friendly to some extent. It has been reported that piezocatalysis can generate H2O2 under mechanical excitation. Therefore, it is promising to carry out the Fenton catalysis utilizing in situ H2O2 generated by piezocatalysis. However, the current piezocatalysis-assisted Fenton (Piezo-Fenton) reaction was realized by adding piezoelectric nanoparticles and Fe(II) ions to pollutant solutions, which would induce more iron-based chemicals that are not easy to recycle. Herein, Fe3O4-BaTiO3 nanocomposites were prepared to demonstrate the feasibility of piezo-Fenton catalysis without the addition of H2O2 or Fe(II) ions. The organic dye degradation efficiency of 98.2% is obtained using Fe3O4-BaTiO3 nanocomposites in the acidic solution, one-third and two-thrid greater than that of pure piezocatalysis and that of iron-based Fenton reaction, respectively. Moreover, since the piezocatalysis process is the rate-determining step of the whole piezo-Fenton reaction, all the H2O2 generated can be consumed. Considering that the solid nanocomposites can be magnetically recycled, piezo-Fenton catalysis leaves no additional chemicals in clean water and thus provides an environmentally friendly and low-cost approach for organic dye degradation.

Experimental and first-principles insights into an enhanced performance of Ru-doped copper phosphate electrocatalyst during oxygen evolution reaction

The oxygen evolution reaction (OER) is a vital half-reaction in many applications, such as the electrochemical H2O splitting, CO2, and N2 conversion processes. The OER involves a four-electron transfer and is a kinetically sluggish reaction that requires additional potential to drive. To enhance the electrochemical performance of the above-mentioned applications, highly efficient, corrosion-resistant, earth-abundant, and eco-friendly electrocatalysts are required. Here, we report a highly porous, minimally Ru-doped copper phosphate electrocatalyst obtained through co-precipitation. The optimized electrocatalyst (5% Ru-doped copper phosphate) exhibits a low overpotential of 340 mV to achieve 10 mA cm−2 compared to copper-based materials, and it remains stable over 20 h. The high performance is attributed to a high electrochemically effective surface area (ECSA) of 30.25 cm2, facilitating effective ion transportation at the electrode/electrolyte interface and excellent electrical conductivity. This result is supported by density functional theory calculations, which demonstrate that ruthenium enhances the electrochemical properties by increasing electronic conductivity, reducing the theoretical overpotential, and influencing the rate-determining step of the oxygen evolution reaction. Herein, the electrocatalyst is attractive for commercialization due to its utilization of minimal ruthenium in earth-abundant electrocatalysts, which offer competitive performance.

N, P codoped hollow carbon prisms for efficient oxidative dehydrogenation reaction with both enhanced activity and selectivity

Carbon materials have stimulated tremendous interest in oxidative dehydrogenation (ODH) of alkane to olefin molecules at low temperature. Unfortunately, its further development has been seriously hindered due to the unsatisfactory catalytic performance. To tackle these challenges, nitrogen and phosphorus codoped hollow carbon prisms (NPC) are designed with controllable surface functional groups through supramolecular pre-assembly and substitution reaction from guanine and hexachlorotriphosphazene. The resultant catalysts can achieve both high catalytic activity (63 % conversion) and styrene selectivity (90 %) in ODH of ethylbenzene, outerperforming previous reported carbon-based catalysts. Structural characterizations, kinetics measurements and theoretical results unravel that nitrogen doping can promote nucleophilicity of –CO, thus improving the catalytic activity. The phosphorus doping not only changes reaction rate-determining step from activation of O2 in N-doped carbon to activation of –C–H bond of EB in N,P-codoped carbon, but also inhibits the formation of electrophilic oxygen species, which enhances selectivity of styrene. The current work provides a facile strategy for preparation of functional NPC catalyst and physical–chemical insights on the structure–activity relationship of NPC catalysts, paving the way for further development of the highly efficient non-metallic catalytic systems.

The effect of hierarchical pore structure SAPO-34 catalyst on the diffusion and reaction behavior in MTO reaction

Establishing the hierarchical pore structure is considered as a feasible approach for enhancing diffusion and improve catalytic efficiency of SAPO-34 zeolite in the methanol-to-olefin process. Nevertheless, under reaction conditions, the correlation among the diffusion behavior in the crystal, coke deposition behavior and catalytic performance of SAPO-34 catalysts with varying pore structures remains to be clarified. Herein, we revealed the structure–activity relationship between the hierarchical pore structure, the catalytic performance and the anti-coke deposition performance of the catalyst in the MTO reaction via the synergy of reaction–diffusion experiments and molecular simulation, then the mechanism of the hierarchical pore SAPO-34 catalyst to eliminate the diffusion limit and improve the accessibility of acid sites was clarified. The results demonstrated that the establishment of a hierarchical pore structure strengthened the diffusion of reactant methanol in the pores, leading to the diffusion resistance being reduced by 5 times and the diffusion coefficient being improved by two orders of magnitude. The key reaction rate-determining step shifted from micropores diffusion to the adsorption of acid sites in hierarchical pores, and the catalytic efficiency of the catalyst was increased by 3 times. Furthermore, with the establishing hierarchical pore technique, the expansion of the accommodation space for coke deposition led to a reduction in the blocking of pores due to coke deposition, particularly around the orifices. Moreover, the accessibility of the reactant molecules to the acid sites within the pores was enhanced, resulting in a balanced ratio between pore blockage and acid site coverage, thereby improving the anti-coke deposition performance of the SAPO-34 catalyst. This work can provide important foundational data and theoretical guidance for the study of reaction–diffusion synergistic interaction in zeolite catalysis reactions.

Human Butyrylcholinesterase Mutants for (-)-Cocaine Hydrolysis: A Correlation Relationship between Catalytic Efficiency and Total Hydrogen Bonding Energy with an Oxyanion Hole.

A combined computational and experimental study has been carried out to explore and test a quantitative correlation relationship between the relative catalytic efficiency (RCE) of human butyrylcholinesrase (BChE) mutant-catalyzed hydrolysis of substrate (-)-cocaine and the total hydrogen bonding energy (tHBE) of the carbonyl oxygen of the substrate with the oxyanion hole of the enzyme in the modeled transition-state structure (TS1), demonstrating a satisfactory linear correlation relationship between ln(RCE) and tHBE. The satisfactory correlation relationship has led us to computationally predict and experimentally confirm new human BChE mutants that have a further improved catalytic activity against (-)-cocaine, including the most active one (the A199S/F227S/S287G/A328W/Y332G mutant) with a 2790-fold improved catalytic efficiency (kcat/KM = 2.5 × 109 min-1 M-1) compared to the wild-type human BChE. Compared to the reference mutant (the A199S/S287G/A328W/Y332G mutant) tested in the reported clinical development of an enzyme therapy for cocaine dependence treatment, this new mutant (with a newly predicted additional F227S mutation) has an improved catalytic efficiency against (-)-cocaine by ∼2.6-fold. The good agreement between the computational and experimental ln(RCE) values suggests that the obtained correlation relationship is robust for computational prediction. A similar correlation relationship could also be explored in studying BChE or other serine hydrolases/esterases with an oxyanion hole stabilizing the carbonyl oxygen in the rate-determining reaction step of the enzymatic hydrolysis of other substrates.

Scaling Relation between the Reduction Potential of Copper Catalysts and the Turnover Frequency for the Oxygen and Hydrogen Peroxide Reduction Reactions.

Changes in the electronic structure of copper complexes can have a remarkable impact on the catalytic rates, selectivity, and overpotential of electrocatalytic reactions. We have investigated the effect of the half-wave potential (E1/2) of the CuII/CuI redox couples of four copper complexes with different pyridylalkylamine ligands. A linear relationship was found between E1/2 of the catalysts and the logarithm of the maximum rate constant of the reduction of O2 and H2O2. Computed binding constants of the binding of O2 to CuI, which is the rate-determining step of the oxygen reduction reaction, also correlate with E1/2. Higher catalytic rates were found for catalysts with more negative E1/2 values, while catalytic reactions with lower overpotentials were found for complexes with more positive E1/2 values. The reduction of O2 is more strongly affected by the E1/2 than the H2O2 rates, resulting in that the faster catalysts are prone to accumulate peroxide, while the catalysts operating with a low overpotential are set up to accommodate the 4-electron reduction to water. This work shows that the E1/2 is an important descriptor in copper-mediated O2 reduction and that producing hydrogen peroxide selectively close to its equilibrium potential at 0.68 V vs reversible hydrogen electrode (RHE) may not be easy.

Ligand effect on switching the rate-determining step of water oxidation in atomically precise metal nanoclusters

The ligand effects of atomically precise metal nanoclusters on electrocatalysis kinetics have been rarely revealed. Herein, we employ atomically precise Au25 nanoclusters with different ligands (i.e., para-mercaptobenzoic acid, 6-mercaptohexanoic acid, and homocysteine) as paradigm electrocatalysts to demonstrate oxygen evolution reaction rate-determining step switching through ligand engineering. Au25 nanoclusters capped by para-mercaptobenzoic acid exhibit a better performance with nearly 4 times higher than that of Au25 NCs capped by other two ligands. We deduce that para-mercaptobenzoic acid with a stronger electron-withdrawing ability establishes more partial positive charges on Au(I) (i.e., active sites) for facilitating feasible adsorption of OH– in alkaline media. X-ray photo-electron spectroscopy and theoretical study indicate a profound electron transfer from Au(I) to para-mercaptobenzoic acid. The Tafel slope and in situ Raman spectroscopy suggest different ligands trigger different rate-determining step for these Au25 nanoclusters. The mechanistic insights reported here can add to the acceptance of atomically precise metal nanoclusters as effective electrocatalysts.