Rate-limiting Step Research Articles

Boosting C-O Bond Cleavage and Reverse Water-Gas Shift Activity via Enriched in-plane Sulfur Vacancies in Single-Layer Molybdenum Disulfide.

The reduction of CO2 to CO provides a promising approach to the production of valuable chemicals through CO2 utilization. However, challenges persist with the rapid deactivation and insufficient activity of catalysts. Herein, we developed a soft-hard dual-template method to synthesize layered MoS2 using inexpensive and scalable templates, enabling facile regulation of sulfur vacancies by controlling the number of layers. The concentration of in-plane vacancies keeps increasing with the reduction of MoS2 layer number, contributing to 100% CO selectivity over single-layer MoS2 and a stable performance over 300-hour reaction at 600 °C. The space-time-yield of CO reached 35.7 gCO gcat-1 h-1, outperforming most current catalysts. Multiple characterizations and theoretical calculations revealed that in-plane sulfur vacancy sites endowed enhanced production of CO via direct dissociation of CO2, showing an intrinsic activity of above 5.8 times higher than that of edge sulfur vacancy sites. The rate-limiting step was shifted from C-O cleavage in edge to sulfur vacancy regeneration in plane with a lower energy barrier. Our findings exemplified the specified design and synthesis of MoS2 for high-temperature CO2 reduction through the effective manipulation of distinct vacancy sites, shedding light on their potential industrial application.

Non-metallic iodine single-atom catalysts with optimized electronic structures for efficient Fenton-like reactions

In this study, we introduce a highly effective non-metallic iodine single-atom catalyst (SAC), referred to as I-NC, which is strategically confined within a nitrogen-doped carbon (NC) scaffold. This configuration features a distinctive C-I coordination that optimizes the electronic structure of the nitrogen-adjacent carbon sites. As a result, this arrangement enhances electron transfer from peroxymonosulfate (PMS) to the active sites, particularly the electron-deficient carbon. This electron transfer is followed by a deprotonation process that generates the peroxymonosulfate radical (SO5•−). Subsequently, the SO5•− radical undergoes a disproportionation reaction, leading to the production of singlet oxygen (1O2). Furthermore, the energy barrier for the rate-limiting step of SO5•− generation in I-NC is significantly lower at 1.45 eV, compared to 1.65 eV in the NC scaffold. This reduction in energy barrier effectively overcomes kinetic obstacles, thereby facilitating an enhanced generation of 1O2. Consequently, the I-NC catalyst exhibits remarkable catalytic efficiency and unmatched reactivity for PMS activation. This leads to a significantly accelerated degradation of pollutants, evidenced by a relatively high observed kinetic rate constant (kobs ~ 0.436 min−1) compared to other metallic SACs. This study offers valuable insights into the rational design of effective non-metallic SACs, showcasing their promising potential for Fenton-like reactions in water treatment applications.

Deciphering and Enhancing Rate-Determining Step of Sodium Deposition towards Ultralow-Temperature Sodium Metal Batteries.

Achieving high ionic conductivity and stable performance at low temperatures remains a significant challenge in sodium-metal batteries (SMBs). In this study, we propose a novel electrolyte design strategy that elucidates the solvation structure-function relationship within mixed solvent systems. A mixture of diglyme and 1,3-dioxolane was developed to optimize the solvation structure towards superior low-temperature electrolyte. Molecular dynamics simulations and Raman spectra results reveal the solvent-separated ion pairs and contact ion pairs dominated solvation structure in the designed electrolyte, displaying a superior ionic conductivity of 1.78×10-3 S cm-1 at -40 °C. Besides, comprehensive kinetic analysis shows Na+ transportation in the electrolyte shows a greater impact on sodium plating than Na+ transport through the solid electrolyte interphase or charge transfer. As a result, the electrolyte enables stable operation for over 12,000 hours in Na||Na cells at -40 °C. In Na||Na2/3Ni1/4Cu1/12Mn2/3O2 full cells, it maintains a high capacity retention of 92.4% over 600 cycles with an initial specific capacity of 89.4 mAh g-1 at -40 °C, and achieves 81.7% capacity retention after 50 cycles with an initial specific capacity of 75.3 mAh g-1 at -78 °C. These results pave the way for the development of high-performance SMBs capable of operating under ultralow temperatures.

Cu-Catalyzed Diastereo- and Enantioselective Synthesis of Borylated Cyclopropanes with Three Contiguous Stereocenters.

Direct synthesis of enantioenriched scaffolds with multiple adjacent stereocenters remains an important yet challenging task. Herein, we describe a highly diastereo- and enantioselective Cu-catalyzed alkylboration of cyclopropenes, with less reactive alkyl iodides as electrophiles, for the efficient synthesis of tetra-substituted borylated cyclopropanes bearing three consecutive stereocenters. This protocol features mild conditions, a broad substrate scope, and good functional group tolerance, affording an array of chiral borylated cyclopropanes in good to high yields with excellent diastereo- and enantioselectivities. Detailed mechanistic experiments and kinetic studies were conducted to elucidate the reaction pathway and the rate-determining step of the reaction. DFT calculations revealed that the π···π stacking interaction between the phenyl groups on the substrate and the phosphorus ligand, along with the smaller distortion in the CuL-Bpin part, contributed to the high diastereo- and enantioselectivities. The synthetic utility of the protocol was showcased by the facile synthesis of some valuable chiral cyclopropanes with multiple chiral centers.

Highly efficient and rapid removal of Congo red dye from textile wastewater using facile synthesized Mg/Ni/Al layered double hydroxide

Layered double hydroxides (LDH) are compounds with unique structures of hydroxide functional groups on their surfaces, and they have the proper arrangement of divalent and trivalent cations to adjust their unique catalytic actions. LDH was synthesized utilizing the co-precipitation technique and was thermally treated at 300 °C. The prepared compounds were chemically and structurally elucidated using FT-IR, XRD, SEM, BET, TG-DTA, and XPS characterization. We found that the thermal treatment of the prepared magnesium/nickel-LDH resulted in dehydration and dehydroxylation in its chemical structure. The crystallinity, the surface area, and the pore volume of the formed meso- and micropores were improved considerably after the thermal treatment. The efficiency of the uptake process was increased from 84 to 97% after the thermal treatment process, and the adsorption process tracked the Freundlich adsorption isotherm and pseudo-second-order kinetic model. The kinetics indicated the occurrence of three stages, and the diffusion of dye molecules into the pores was the rate-determining step. Different real water sample treatments showed the applicability of the thermally treated Mg/Ni/Al-LDH in the treatment process under optimized conditions. The presented mechanism of the uptake process using the prepared compounds comprises several interactions between the dye molecules and the thermally treated Mg/Ni/Al-LDH. The study presented the new application for Mg/Ni/Al-LDH in the as-prepared and thermally treated forms to uptake Congo-red (CR) dye from textile effluents.

Improved Ammonia Synthesis and Energy Output from Zinc-Nitrate Batteries by Spin-State Regulation in Perovskite Oxides.

Electrocatalytic nitrate reduction to ammonia (eNRA) is a promising route toward environmental sustainability and clean energy. However, its efficiency is often limited by the slow conversion of intermediates due to spin-forbidden processes. Here, we introduce a novel A-site high-entropy strategy to develop a new perovskite oxide (La0.2Pr0.2Nd0.2Ba0.2Sr0.2)CoO3-δ (LPNBSC) for eNRA. The LPNBSC possesses a higher concentration of high-spin (HS) cobalt-active centers, resulting from an increased concentration of [CoO5] structural motifs compared to conventional LaCoO3. Consequently, this material exhibits a significantly improved electrocatalytic performance toward ammonia (NH3) production, resulting in a 3-fold increase in yield rate (129 μmol h-1 mgcat.-1) and a 2-fold increase in Faradaic efficiency (FE, 76%) compared to LaCoO3 at the optimal potential. Furthermore, the LPNBSC-based Zn-nitrate battery reaches a maximum FE of 82% and an NH3 yield rate of 57 μmol h-1 cm-2. Density functional theory calculations reveal that A-site high-entropy management in perovskites facilitates nitrate activation and potentially optimizes the thermodynamic rate-determining step of the eNRA process, namely, *HNO3 + H+ + e- → *NO2 + H2O. This work presents an efficient concept for modulating the spin state of the B-site metal in perovskites and offers valuable insights for the design of high-performance eNRA catalysts.

Enhancing quality and yield of recombinant secretory IgA antibodies in Nicotiana benthamiana by endoplasmic reticulum engineering.

The production of complex multimeric secretory immunoglobulins (SIgA) in Nicotiana benthamiana leaves is challenging, with significant reductions in complete protein assembly and consequently yield, being the most important difficulties. Expanding the physical dimensions of the ER to mimic professional antibody-secreting cells can help to increase yields and promote protein folding and assembly. Here, we expanded the ER in N. benthamiana leaves by targeting the enzyme CTP:phosphocholine cytidylyltransferase (CCT), which catalyses the rate-limiting step in the synthesis of the key membrane component phosphatidylcholine (PC). We used CRISPR/Casto perform site-directed mutagenesis of each of the three endogenous CCT genes in N. benthamiana by introducing frame-shifting indels to remove the auto-inhibitory C-terminal domains. We generated stable homozygous lines of N. benthamiana containing different combinations of the edited genes, including plants where all three isofunctional CCT homologues were modified. Changes in ER morphology in the mutant plants were confirmed by in vivo confocal imaging and substantially increased the yields of two fully assembled SIgAs by prolonging the ER residence time and boosting chaperone accumulation. Through a combination of ER engineering with chaperone overexpression, we increased the yields of fully assembled SIgA by an order of magnitude, reaching almost 1 g/kg fresh leaf weight. This strategy removes a major roadblock to producing SIgA and will likely facilitate the production of other complex multimeric biopharmaceutical proteins in plants.

Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study

Hydrogenation and dehydrogenation reactions are fundamental in chemistry and essential for all living organisms. We employ density functional theory (DFT) to understand the reaction mechanism of the oxidative dehydrogenation (ODH) of the pyridyl-amine complex [FeIIIL3]3+ (L3, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanonane) to the mono-imine complex [FeIIL4]2+ (L4, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanon-1-ene) in the presence of dioxygen. The nitrogen radical [FeIIL3N8•]2+, formed by deprotonation of [FeIIIL3]3+, plays a crucial role in the reaction mechanism derived from kinetic studies. O2 acts as an oxidant and is converted to H2O. Experiments with the deuterated ligand L3 reveal a primary C-H kinetic isotope effect, kCH/kCD = 2.30, suggesting C-H bond cleavage as the rate-determining step. The DFT calculations show that (i) 3O2 abstracts a hydrogen atom from the α-pyridine aliphatic C-H moiety, introducing a double bond regio-selectively at the C7N8 position, via the hydrogen atom transfer (HAT) mechanism, (ii) O2 does not coordinate to the iron center to generate a high-valent Fe oxo species observed in enzymes and biomimetic complexes, and (iii) the experimental activation parameters (ΔH≠ = 20.38 kcal mol−1, ΔS≠ = −0.018 kcal mol−1 K−1) fall within in the range of values reported for HAT reactions and align well with the computational results for the activated complex [FeIIL3N8•]2+···3O2.

Oxidation of N,N-Dimethylhydroxylamine by Hexachloroiridate(IV).

The oxidation of (CH3)2NOH (DMH, N,N-dimethylhydroxylamine) is of interest because of the use of this reagent in actinide separations. Here, we report on the aqueous oxidation of DMH by [IrCl6]2-, a classic outer-sphere one-electron oxidant. The reaction is subject to adventitious catalysis by Fe2+ and Cu2+, and this catalysis can be suppressed with 1 mM oxalate. The uncatalyzed reaction yields [IrCl6]3- and nitrone (CH3)N(O)CH2. The rate law has two terms: one corresponding to oxidation of (CH3)2NOH and the other to oxidation of (CH3)2NO-. A mechanism is inferred in which the rate-limiting steps are electron-transfer oxidations of these two DMH forms, leading to their corresponding radicals. The nitrone arises from the oxidation of the DMH radical, (CH3)2NO·.

Modulation of RuO2 Nanocrystals with Facile Annealing Method for Enhancing the Electrocatalytic Activity on Overall Water Splitting in Acid Solution.

RuO2-based materials are considered an important kind of electrocatalysts on oxygen evolution reaction and water electrolysis, but the reported discrepancies of activities exist among RuO2 electrocatalysts prepared via different processes. Herein, a highly efficient RuO2 catalysts via a facile hydrolysis-annealing approach is reported for water electrolysis. The RuO2 catalyst dealt with at 200 °C (RuO2-200) performs the highest activities on both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acid with overpotentials of 200 mV for OER and 66 mV for HER to reach a current density of 100 mA cm-2 as well as stable operation for100 h. The high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) characterizations show that the activities of as-prepared RuO2 rely on the hydroxide group/lattice oxygen (OH-/O2-) ratio, size, and crystalline of RuO2. The density functional theory (DFT) calculation also reveal that the OH- would enhance the activities of RuO2 for HER and OER via modifying the electronic structure to facilitate intermediate adsorption, thereby reducing the energy barrier of the rate-determining step. The water electrolysis by using RuO2-200 as the catalyst on both anode and cathode demonstrates a stable generation of hydrogen and oxygen with high Faradic efficiency at a current density of ≈30 mA cm-2 and a potential of below 1.47 V.

Revealing the Potential-Dependent Rate-Determining Step of Oxygen Reduction Reaction on Single-Atom Catalysts.

Single-atom catalysts (SACs) have attracted widespread attention due to their potential to replace platinum-based catalysts in achieving efficient oxygen reduction reaction (ORR), yet the rational optimization of SACs remains challenging due to their elusive reaction mechanisms. Herein, by employing ab initio molecular dynamics simulations and a thermodynamic integration method, we have constructed the potential-dependent free energetics of ORR on a single iron atom catalyst dispersed on nitrogen-doped graphene (Fe-N4/C) and further integrated these parameters into a microkinetic model. We demonstrate that the rate-determining step (RDS) of the ORR on SACs is potential-dependent rather than invariant within the operative potential range. Specifically, under the charge-neutral condition, the RDS is calculated to be water desorption with the highest barrier, while as the potential increases, it gradually transitions to the protonation of *OH species, O2* species, and O* species, regardless of the protonation of *OH species as the potential-determining step. Moreover, we reveal the critical role of the dynamic adsorption of axially adsorbed water in facilitating the release of the single-atom site, thus enhancing the ORR rate. Our work has resolved the long-standing controversies over the RDS of ORR on SACs and implies that the step with the lowest exothermicity is not always synonymous with the RDS, highlighting the importance of examining the kinetic barriers under realistic potential conditions for understanding the electrocatalytic performance.

What Factors Determine the Brevione B Desaturation Mechanism in the Nonheme Iron Dioxygenase BrvJ?

The natural product synthesis of brevione J undergoes a cascade of reactions including an oxidative desaturation and a ring-expansion. The C1-C2 desaturation of brevione B is catalyzed by the nonheme iron dioxygenase BrvJ using one molecule of O2 and a-ketoglutarate (aKG). However, whether the subsequent oxidative ring expansion reaction is also catalyzed by the same enzyme is unknown and remains controversial. To gain insight into the mechanism of brevione J biosynthesis a computational study is reported here using molecular dynamics and density functional theory approaches. The work predicts that both cycles can proceed in the same protein structure on an iron center with O2 and aKG for each cycle. The rate-determining step is a hydrogen atom abstraction step in both reaction cycles. Interestingly, the OH rebound barriers are high in energy in cycle 1 due to stereochemical interactions and substrate positioning that enable an efficient desaturation reaction.

In Situ Spectroscopic Probing of the Hydroxylamine Pathway of Electrocatalytic Nitrate Reduction on Iron-Oxy-Hydroxide.

Crystalline γ-FeO(OH) dominantly possessing ─OH terminals (𝛾-FeO(OH)c), polycrystalline γ-FeO(OH) containing multiple ─O, ─OH, and Fe terminals (𝛾-FeO(OH)pc), and α-Fe2O3 majorly containing ─O surface terminals are used as electrocatalysts to study the effect of surface terminals on electrocatalytic nitrate reduction reaction (eNO3RR) selectivity and stabilization of reaction intermediates. Brunauer-Emmett-Teller analysis and electrochemically determined surface area suggest a high active surface area of 117.79 m2 g-1 (ECSA: 0.211 cm2) for 𝛾-FeO(OH)c maximizing the surface accessibility for nitrate adsorption and exhibiting selective eNO3RR to NH3 at pH 7 with a yield rate 18.326mg h-1 cm-2, >85% Faradaic efficiency (FE), and at least nine-times catalyst-recyclability. 15N- and D-labeling combined with in situ IR and Raman studies validate the adsorption of nitrate ions on the ─OH terminals of 𝛾-FeO(OH)c and the generation of nitrite and hydroxyl amine as eNO3RR intermediates. A kinetic isotope effect (KIE) value of 2.1 indicates H2O as the proton source and proton-coupled electron transfer as the rate-limiting step. The rotating-ring disk electrochemical (RRDE) study and subsequent Koutecký-Levich analysis reveal the electron-transfer rate constant (k) for the 2e- reduction of nitrate to nitrite is 5.7 × 10-6cm s-1. This study provides direct evidence of the hydroxyl amine formation as the dominant pathway of eNO3RR on γ-FeO(OH).

Evaluation of pig farming residue as substrate for biomethane production via anaerobic digestion

Abstract Livestock farming and manure management contribute substantially to greenhouse gas (GHG) emissions in agriculture. Anaerobic digestion (AD) of manure is a promising strategy for mitigating these emissions. This study aimed to assess the biomethane potential (BMP) of various types of pig slurry, investigate factors that influence biomethane production, analyze degradation kinetics, and propose AD process optimization approaches. Thus, substrate analysis, BMP tests in batch assays, kinetic modeling, and principal component analysis (PCA) were conducted. In order to further quantify the effects of different substrate qualities in full-scale operation, biomethane production was simulated under steady-state conditions. Results indicated that piglet slurry had the highest volatile solids (VS)–specific BMP (203 ± 72 L kg−1 VS), followed by mixed slurry (202 ± 132 L kg−1 VS), fattening pig slurry (117 ± 56 L kg−1 VS), and sow slurry (86 ± 17 L kg−1 VS). The PCA revealed different substrate types and significant roles for VS, crude fat, volatile fatty acids concentration, and the carbon/nitrogen ratio in achieving high BMPs. First-order two-step kinetic modeling identified hydrolysis as the rate-limiting step, showing a determinant of rate-limiting step of < 0 for each sample. The simulation of continuous operation revealed notable differences in daily biomethane production (36.7–42.7 L day−1) between the different slurries at the same hydraulic retention time and BMP. This research underscores the variability in pig slurry characteristics, exemplified by a total solids range of 1.4–12.1%, and provides crucial insights for optimizing AD processes in livestock waste management.

A Density Functional Theory (DFT) Modeling Study of NO Reduction by CO over Graphene-Supported Single-Atom Ni Catalysts in the Presence of CO2, SO2, O2, and H2O.

The mechanisms of NO reduction by CO over nitrogen-doped graphene (N-graphene)-supported single-atom Ni catalysts in the presence of O2, H2O, CO2, and SO2 have been studied via density functional theory (DFT) modeling. The catalyst is represented by a single Ni atom bonded to four N atoms on N-graphene. Several alternative reaction pathways, including adsorption of NO on the Ni site, direct reduction of NO by CO, decomposition of NO to N2O followed by reduction of N2O to N2, formation of active oxygen radical O*, and reduction of O* by CO, were hypothesized and the energy barrier corresponding to each of the reaction steps was calculated using DFT. The most probable pathway was found to be that NO adsorbed on the Ni site decomposes via the Langmuir-Hinshelwood mechanism to form N2O and subsequently N2, leaving an active oxygen radical (O*) on the surface, which is then reduced by CO. The large adsorption energy of NO on the Ni site results in strong resistance to CO2, SO2, O2, and water vapor. The activation energy of N2O reduction to N2 was found to be larger than those of NO decomposition to N2O and active oxygen radical reduction by CO, illustrating that the step of N2O reduced to N2 is the rate-controlling step.

Efficient Oxidative Removal of Indoor Formaldehyde Using Functionalized Activated Alumina.

Formaldehyde (HCHO) has become a significant indoor air pollutant, arising from the widespread use of decorative and construction materials. Adsorption is the most convenient method for HCHO removal. However, the current adsorption is limited by the current low adsorption capacity and desorption. Herein, activated alumina (γ-Al2O3) loaded with permanganate was proposed for the efficient oxidative removal of indoor HCHO. The results demonstrate that the permanganate-containing alumina-based pellets (PAP) with 75% of alumina (PAP-75) displayed the highest adsorption capacity of 10,800 μg g-1. This high adsorption capacity is mainly attributed to the presence of numerous pore structures within the pellets, good dispersion of permanganate on the surface and inside the spheres, abundant surface-active sites, and high porosity. The adsorption kinetics explains that the chemisorption, intraparticle diffusion, and film diffusion are the primary rate-controlling steps. This study provides an effective strategy for further improving alumina-based adsorption materials for HCHO removal.

Adsorption of TDS and chloride ions from partially treated tannery wastewater using activated coffee husk

The aim of this study was to treat tannery wastewater by using activated carbon derived from coffee husk to effectively remove total dissolved solids (TDS) and chloride ions. The tannery’s wastewater discharged to the environment is often untreated or partially treated. Due to the current worldwide water shortage, it is essential to develop sustainable strategies for managing water resources, such as recycling and reusing after treatment. Therefore, finding cost-effective and eco-friendly methods to purify contaminated water is crucial. In the study, activated coffee husk has been found to be effective for removing TDS and chloride ions from tannery wastewater. Activated coffee husk was evaluated by conducting experiments with chemical activation using phosphoric acid. The carbonized coffee husk was then used to remove total dissolved solids (TDS) and chloride ions from tannery wastewater. To investigate the adsorption process of TDS and chloride ions on the activated coffee husk surface, contact time (1–3 h), pH (5–9), and adsorbent dosage (1–3 g/L) were considered. The activated coffee husk was characterized using SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared Spectroscopy), BET (Brunauer Emmett Teller), and XRD (X-ray diffraction). The adsorption isotherm and kinetics were determined using different models. Design expert was used to optimize TDS and chloride ions adsorption and the optimal conditions were 2.38 h of contact time, pH of 7.19, and 2.54 g/L adsorbent dosage. The removal efficiency of 77.88% for chloride ions and 72.73% for TDS indicates a higher efficacy compared to traditional methods using commercial activated carbon. The Langmuir isothermal model of R2 value for both TDS and chloride ions were 0.9969 and 0.9504 respectively. The adsorption kinetics of TDS and chloride ions follow a pseudo-second-order model, indicating that chemisorption is the rate-limiting step in the process.

Key Interaction Changes Determine the Activation Process of Human Parathyroid Hormone Type 1 Receptor.

The parathyroid hormone type 1 receptor (PTH1R) plays a crucial role in modulating various physiological functions and is considered an effective therapeutic target for osteoporosis. However, a lack of detailed molecular and energetic information about PTH1R limits our comprehensive understanding of its activation process. In this study, we performed computational simulations to explore key events in the activation process, such as conformational changes in PTH1R, Gs protein coupling, and the release of guanosine diphosphate (GDP). Our analysis identified kinetic information, including the rate-determining step, transition state, and energy barriers. Free-energy and structural analyses revealed that GDP could be released from the Gs protein when the binding cavity is partially open. Additionally, we predicted important residues, including potential pathogenic mutations, and verified their significance through site-directed mutations. These findings enhance our understanding of class B GPCR activation mechanisms. Furthermore, the methodology employed in this study can be applied to other biophysical systems.

Cobalt(II)-Catalyzed C−H Deuteriomethoxylation of Benzamides with CD3OD

Herein, we report a practical example of salicylaldehyde-based cobalt-catalyzed C−H deuteriomethoxylation of benzamides using deuterated methanol, facilitated by 8-aminoquinoline as a directing group. The salicylaldehyde-based cobalt catalyst is user-friendly, and the reaction exhibits broad functional group tolerance, accommodating benzene, heterocycles, and naphthalene rings. The synthetic utility of this methodology was demonstrated through a gram-scale reaction and the subsequent removal of the 8-aminoquinoline directing group to yield deuteriomethoxylated benzoic acid. Preliminary mechanistic studies suggest that C−H activation is not the rate-determining step of the reaction.

Identifying the Bifunctional Mechanism in Alkaline Water Electrolysis by Lewis Pairs at the Single-Atom Scale.

The bifunctional mechanism, involving multiactive compositions to simultaneously dissociate water molecules and optimize intermediate adsorption, has been widely used in the design of catalysts to boost water electrolysis for sustainable hydrogen energy production but remains debatable due to difficulties in accurately identifying the reaction process. Here, we proposed the concept of well-defined Lewis pairs in single-atom catalysts, with a unique acid-base nature, to comprehensively understand the exact role of multiactive compositions in an alkaline hydrogen evolution reaction. By facilely adjusting active moieties, the induced synergistic effect between Lewis pairs (M-P/S/Cr pairs, M = Ru, Ir, Pt) can significantly facilitate the cleavage of the H-OH bond and accelerate the removal of intermediates, thereby switching the rate-determining step from the Volmer step to the Heyrovsky step. Moreover, the representative Ru-P Lewis pairs deliver an impressive 266 h durability at a high industrial current density of 2 A cm-2 without activity decay in anion-exchange membrane water electrolysis, and the concept can be extended to modify commercial noble-metal-based catalysts for performance enhancement. This work not only sheds light on the important effect of the bifunctional mechanism in alkaline water electrolysis at the single-atom scale but also offers a universal descriptor for the rational design of advanced catalysts.