Structural tuning of heterogeneous molecular catalysts for electrochemical energy conversion

Atomic Gap-State Engineering of MoS2 for Alkaline Water and Seawater Splitting

Transition-metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), have emerged as a generation of nonprecious catalysts for the hydrogen evolution reaction (HER), largely due to their theoretical hydrogen adsorption energy close to that of platinum. However, efforts to activate the basal planes of TMDs have primarily centered around strategies such as introducing numerous atomic vacancies, creating vacancy-heteroatom complexes, or applying significant strain, especially for acidic media. These approaches, while potentially effective, present substantial challenges in practical large-scale deployment. Here, we report a gap-state engineering strategy for the controlled activation of S atom in MoS2 basal planes through metal single-atom doping, effectively tackling both efficiency and stability challenges in alkaline water and seawater splitting. A versatile synthetic methodology allows for the fabrication of a series of single-metal atom-doped MoS2 materials (M1/MoS2), featuring widely tunable densities with each dopant replacing a Mo site. Among these (Mn1, Fe1, Co1, and Ni1), Co1/MoS2 demonstrates outstanding HER performance in both alkaline and seawater alkaline media, with overpotentials at a mere 159 and 164 mV at 100 mA cm-2, and Tafel slopes at 41 and 45 mV dec-1, respectively, which surpasses all reported TMD-based nonprecious materials and benchmark Pt/C catalysts in HER efficiency and stability during seawater splitting, which can be attributed to an optimal gap-state modulation associated with sulfur atoms. Experimental data correlating doping density and dopant identity with HER performance, in conjunction with theoretical calculations, also reveal a descriptor linked to near-Fermi gap state modulation, corroborated by the observed increase in unoccupied S 3p states.

Localized Oxidative Catalytic Reactions Triggered by Cavitation Bubbles Confinement on Copper Oxide Microstructured Particles

Efficient energy transfer management in catalytic processes is crucial for overcoming activation energy barriers while minimizing costs and CO2 emissions. We exploit here a concept of CuO particle design with multiple gas-stabilizing sites, engineered to function as cavitation nuclei and catalysts. This concept facilitates the selective and efficient acoustic energy transfer directly to the catalyst surface, avoiding the undesired dissipation of acoustic energy into the bulk solution while demonstrating superior cavitation properties at lower acoustic pressure amplitudes. Utilizing a chemical thermometric approach, we demonstrate that the local temperature on the surface of our CuO particles during cavitation bubble implosions can create an effective equivalent temperature of about 360 °C. This temperature effect facilitates the efficient catalysis of oxidative reactions using an organic pollutant probe molecule. Density functional theory (DFT) calculations were used to assess the decomposition of H2O2 and of pollutant probe molecule on CuO (111). Our work represents a significant advance in sonocatalytic systems, promising efficient energy use in catalytic reactions.

Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

Testing mixed metal bimetallic, and monometallic, cryptates for electrocatalytic hydrogen evolution

Appropriately designed catalysts help to minimise the energy required to convert the energy-poor feedstock H2O into energy-rich molecular H2. Herein, two families of pyridazine-based cryptates, mononuclear [MIILi](BF4)2 and mixed metal dinuclear [MIICuILi](BF4)3 (M = Fe, Co, Cu or Zn; Li is the Schiff base cryptand made by 2 : 3 condensation of tris(2-aminoethyl)amine and 3,6-diformylpyridazine), are investigated as potential electrocatalysts for the hydrogen evolution reaction (HER) in MeCN with acetic acid as the proton source. The synthesis and structures of a new mixed metal cryptate, [ZnIICuILi](BF4)3, and the tetrafluoroborate analogue of the previously reported perchlorate salt of the mono-zinc cryptate, [ZnIILi](BF4)2·0.5H2O, are reported. Electrocatalytic HER testing showed that a deposit forms on the glassy carbon working electrode during electrolysis and it is the active species responsible for the very modest activity observed. The deposits formed by the heterobinuclear cryptates had higher activities (2.0 < TON2h < 3.5) than the deposits formed by the mononuclear cryptates (TON2h < 0.75). But unfortunately the control, using CuI(MeCN)4BF4, had a similar TON2h (2.3) to those seen for the heterobinculear cryptates, which indicates that it is the deposit formed by the CuI cation present in the heterobinuclear cryptates that is likely responsible for the observed, very modest, HER activity.

Recent Advances in Immobilizing and Benchmarking Molecular Catalysts for Artificial Photosynthesis

Transition metal complexes have been widely used as catalysts or chromophores in artificial photosynthesis. Traditionally, they are employed in homogeneous settings. Despite their functional versatility and structural tunability, broad industrial applications of these catalysts are impeded by the limitations of homogeneous catalysis such as poor catalyst recyclability, solvent constraints (mostly organic solvents), and catalyst durability. Over the past few decades, researchers have developed various methods for molecular catalyst heterogenization to overcome these limitations. In this review, we summarize recent developments in heterogenization strategies, with a focus on describing methods employed in the heterogenization process and their effects on catalytic performances. Alongside the in-depth discussion of heterogenization strategies, this review aims to provide a concise overview of the key metrics associated with heterogenized systems. We hope this review will aid researchers who are new to this research field in gaining a better understanding.

Electrolyte Composition-Dependent Product Selectivity in CO2 Reduction with a Porphyrinic Metal-Organic Framework Catalyst

A copper porphyrin-derived metal-organic framework electrocatalyst, FICN-8, was synthesized and its catalytic activity for CO2 reduction reaction (CO2RR) was investigated. FICN-8 selectively catalyzed electrochemical reduction of CO2 to CO in anhydrous acetonitrile electrolyte. However, formic acid became the dominant CO2RR product with the addition of a proton source to the system. Mechanistic studies revealed the change of major reduction pathway upon proton source addition, while catalyst-bound hydride (*H) species was proposed as the key intermediate for formic acid production. This work highlights the importance of electrolyte composition on CO2RR product selectivity.

Insight into Impacts of π-π Assembly on Phthalocyanine Based Heterogeneous Molecular Electrocatalysis

Electrochemical CO2 reduction (CO2R) to feedstocks competes with the hydrogen evolution reaction (HER). Cobalt phthalocyanine (CoPc) immobilized onto carbon driven by π-π interaction represents a classical type of heterogeneous molecular catalyst for CO2R. However, the impacts of π conjugation on the electrocatalysis have not been clarified. Herein, the electrochemical properties of CoPc were investigated by comparison of its analogue to 2,3-naphthalocyanine cobalt (NapCo) having extended π conjugation. It is found that CoPc is redox-active on carbon to provide low oxidized Co sites for improving the CO2R activity and selectivity, while NapCo on carbon turned out to be redox-inert leading to lower performance. In addition, the redox-mediated mechanism for CO2R on CoPc tends to operate with increasing electrolyte alkalinity, which further enhances the reaction selectivity. We speculated that moderate π conjugation allows the redox-mediated mechanism on CoPc, which is critical to promote CO2R performance while depressing the competing HER.

Subnanometric Osmium Clusters Confined on Palladium Metallenes for Enhanced Hydrogen Evolution and Oxygen Reduction Catalysis

Highly efficient, cost-effective, and durable electrocatalysts, capable of accelerating sluggish reaction kinetics and attaining high performance, are essential for developing sustainable energy technologies but remain a great challenge. Here, we leverage a facile heterostructure design strategy to construct atomically thin Os@Pd metallenes, with atomic-scale Os nanoclusters of varying geometries confined on the surface layer of the Pd lattice, which exhibit excellent bifunctional properties for catalyzing both hydrogen evolution (HER) and oxygen reduction reactions (ORR). Importantly, Os5%@Pd metallenes manifest a low η10 overpotential of only 11 mV in 1.0 M KOH electrolyte (HER) as well as a highly positive E1/2 potential of 0.92 V in 0.1 M KOH (ORR), along with superior mass activities and electrochemical durability. Theoretical investigations reveal that the strong electron redistribution between Os and Pd elements renders a precise fine-tuning of respective d-band centers, thereby guiding adsorption of hydrogen and oxygen intermediates with an appropriate binding energy for the optimal HER and ORR.

Modulating the Electronic Structure of Cobalt in Molecular Catalysts via Coordination Environment Regulation for Highly Efficient Heterogeneous Nitrate Reduction

Ammonia (NH3) is pivotal in modern industry and represents a promising next-generation carbon-free energy carrier. Electrocatalytic nitrate reduction reaction (eNO3RR) presents viable solutions for NH3 production and removal of ambient nitrate pollutants. However, the development of eNO3RR is hindered by lacking the efficient electrocatalysts. To address this challenge, we synthesized a series of macrocyclic molecular catalysts for the heterogeneous eNO3RR. These materials possess different coordination environments around metal centers by surrounding subunits. Consequently, electronic structures of the active centers can be altered, enabling tunable activity towards eNO3RR. Our investigation reveals that metal center with an N2(pyrrole)-N2(pyridine) configuration demonstrates superior activity over the others and achieves a high NH3 Faradaic efficiency (FE) of over 90 % within the tested range, where the highest FE of approximately 94 % is obtained. Furthermore, it achieves a production rate of 11.28 mg mgcat -1 h-1, and a turnover frequency of up to 3.28 s-1. Further tests disclose that these molecular catalysts with diverse coordination environments showed different magnetic moments. Theoretical calculation results indicate that variated coordination environments can result in a d-band center variation which eventually affects rate-determining step energy and calculated magnetic moments, thus establishing a correlation between electronic structure, experimental activity, and computational parameters.

Two Birds with One Stone: Contemporaneously Enhancing OER Catalytic Activity and Stability for Dual-Phase Medium-Entropy Metal Sulfides

Transition metal-based sulfides exhibit remarkable potential as electrocatalysts for oxygen evolution reaction (OER) due to the unique intrinsic structure and physicochemical characteristics. Nevertheless, currently available sulfide catalysts based on transition metals face a bottleneck in large-scale commercial applications owing to their unsatisfactory stability. Here, the first fabrication of (FeCoNiMn2 )S2 dual-phase medium-entropy metal sulfide (dp-MEMS) is successfully achieved, which demonstrated the expected optimization of stability in the OER process. Benefiting from the "cell wall" -like structure and the synergistic effect in medium-entropy systems, (FeCoNiMn2 )S2 dp-MEMS delivers an exceptionally low overpotential of 169 and 232 mV at current densities of 10 and 100 mA cm-2 , respectively. The enhancement mechanism of catalytic activity and stability is further validated by density functional theory (DFT) calculations. Additionally, the rechargeable Zn-air batteries integrated with FeCoNiMn2 )S2 dp-MEMS exhibit remarkable performance outperforming the commercial catalyst (Pt/C+RuO2 ). This work demonstrates that the dual-phase medium-entropy metal sulfide-based catalysts have the potential to provide a greater application value for OER and related energy conversion systems.

Second Coordination Sphere Effect Shifts CO2 to CO Reduction by Iron Porphyrin from Fe0 to FeI

Iron porphyrins are among the most studied molecular catalysts for carbon dioxide (CO2 ) reduction and their reactivity is constantly being enhanced through the implementation of chemical functionalities in the second coordination sphere inspired by the active sites of enzymes. In this study, we were intrigued to observe that a multipoint hydrogen bonding scheme provided by embarked urea groups could also shift the redox activation step of CO2 from the well-admitted Fe(0) to the Fe(I) state. Using EPR, resonance Raman, IR and UV-Visible spectroscopies, we underpinned a two-electron activation step of CO2 starting from the Fe(I) oxidation state to form, after protonation, an Fe(III)-COOH species. The addition of another electron and a proton to the latter species converged to the cleavage of a C-O bond with the loss of water molecule resulting in an Fe(II)-CO species. DFT analyses of these postulated intermediates are in good agreement with our collected spectroscopic data, allowing us to propose an alternative pathway in the catalytic CO2 reduction with iron porphyrin catalyst. Such a remarkable shift opens new lines of research in the design of molecular catalysts to reach low overpotentials in performing multi-electronic CO2 reduction catalysis.

Unlocking the Transition of Electrochemical Water Oxidation Mechanism Induced by Heteroatom Doping

Heteroatom doping has emerged as a highly effective strategy to enhance the activity of metal-based electrocatalysts toward the oxygen evolution reaction (OER). It is widely accepted that the doping does not switch the OER mechanism from the adsorbate evolution mechanism (AEM) to the lattice-oxygen-mediated mechanism (LOM), and the enhanced activity is attributed to the optimized binding energies toward oxygen intermediates. However, this seems inconsistent with the fact that the overpotential of doped OER electrocatalysts (<300 mV) is considerably smaller than the limit of AEM (>370 mV). To determine the origin of this inconsistency, we select phosphorus (P)-doped nickel-iron mixed oxides as the model electrocatalysts and observe that the doping enhances the covalency of the metal-oxygen bonds to drive the OER pathway transition from the AEM to the LOM, thereby breaking the adsorption linear relation between *OH and *OOH in the AEM. Consequently, the obtained P-doped oxides display a small overpotential of 237 mV at 10 mA cm-2 . Beyond P, the similar pathway transition is also observed on the sulfur doping. These findings offer new insights into the substantially enhanced OER activity originating from heteroatom doping.

Enlarging the Ni-O Bond Polarizability in a Phosphorene-Hosted Metal-Organic Framework for Boosted Water Oxidation Electrocatalysis

The emerging lattice-oxygen oxidation mechanism (LOM) presents attractive opportunities for breaking the scaling relationship to boost oxygen evolution reaction (OER) with the direct OLattice-*O interaction. However, currently the LOM-triggering rationales are still debated, and a streamlined physicochemical paradigm is extremely desirable for the design of LOM-defined OER catalysts. Herein, a Ni metal-organic framework/black phosphorene (NiMOF/BP) heterostructure is theoretically profiled and constructed as a catalytic platform for the LOM-derived OER studies. It is found that the p-type BP host can enlarge the Ni-O bond polarizability of NiMOF through the Ni-O bond stretching and Ni valence declining synergically. Such an enlarged bond polarizability will in principle alleviate the lattice oxygen confinement to benefit the LOM pathway and OER performance. As a result, the optimized NiMOF/BP catalyst exhibits promising OER performance with a low overpotential of 260 mV at 10 mA cm-2 and long-term stability in 1 M KOH electrolyte. Both experiment and calculation results suggest the activated LOM pathway with a more balanced step barrier in the NiMOF/BP OER catalyst. This research puts forward Ni-O bond polarizability as the criterion to design LOM-scaled electrocatalysts for water oxidation.

(FeMnCe)-co-doped MOF-74 with significantly improved performance for overall water splitting

Developing inexpensive electrocatalysts with high activity and stability is of great value for overall water splitting. In this work, we designed a series of 3d-4f (FeMnCe)-trimetallic MOF-74 with different ratios of 3d- and 4f-metal centers. Among them, FeMn6Ce0.5-MOF-74/NF exhibited the best electrocatalytic performance for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline solution. It only requires a low overpotential of 281 mV@100 mA cm-2 for OER and 186 mV@-10 mA cm-2 for HER in 1 M KOH. With FeMn6Ce0.5-MOF-74/NF as the anode and cathode in the overall water splitting system, only 1.65 V is needed to deliver a current density of 10 mA cm-2. In particular, for the as-fabricated FeMn6Ce0.5-MOF-74/NF||Pt/C cell unit, only 1.40 V is needed to achieve 10 mA cm-2. Therefore, the successful design of 3d-4f mixed-metallic MOF-74 provides a new viewpoint to develop highly efficient non-precious metal electrocatalysts.

Isolation of Highly Reactive Cobalt Phthalocyanine via Electrochemical Activation for Enhanced CO2 Reduction Reaction

Electrochemical CO₂ -to-CO conversion offers an attractive and efficient route to recycle CO₂ greenhouse gas. Molecular catalysts, like CoPc, are proved to be possible replacement for precious metal-based catalysts. These molecules, a combination of metal center and organic ligand molecule, may evolve into single atom structure for enhanced performance; besides, the manipulation of molecules' behavior also plays an important role in mechanism research. Here, in this work, the structure evolution of CoPc molecules is investigated via electrochemical-induced activation process. After numbers of cyclic voltammetry scanning, CoPc molecular crystals become cracked and crumbled, meanwhile the released CoPc molecules migrate to the conductive substrate. Atomic-scale HAADF-STEM proves the migration of CoPc molecules, which is the main reason for the enhancement in CO₂ -to-CO performance. The as-activated CoPc exhibits a maximum FE_CO of 99% in an H-type cell and affords a long-term durability at 100 mA cm^-2 for 29.3 h in a membrane electrode assembly reactor. Density-functional theory (DFT) calculation also demonstrates a favorable CO₂ activation energy with such an activated CoPc structure. This work provides a different perspective for understanding molecular catalysts as well as a reliable and universal method for practical utilization.

Oxygen-Bridged Stabilization of Single Atomic W on Rh Metallenes for Robust and Efficient pH-Universal Hydrogen Evolution

Highly efficient and durable electrocatalysts are of the utmost importance for the sustainable generation of clean hydrogen by water electrolysis. Here, we present a report of an atomically thin rhodium metallene incorporated with oxygen-bridged single atomic tungsten (Rh-O-W) as a high-performance electrocatalyst for pH-universal hydrogen evolution reaction. The Rh-O-W metallene delivers ascendant electrocatalytic HER performance, characterized by exceptionally low overpotentials, ultrahigh mass activities, excellent turnover frequencies, and robust stability with negligible deactivation, in pH-universal electrolytes, outperforming that of benchmark Pt/C, Rh/C and numerous other reported precious-metal HER catalysts. Interestingly, the promoting feature of -O-W single atomic sites is understood via operando X-ray absorption spectroscopy characterization and theoretical calculations. On account of electron transfer and equilibration processes take place between the binary components of Rh-O-W metallenes, fine-tuning of the density of states and electron localization at Rh active sites is attained, hence promoting HER via a near-optimal hydrogen adsorption.

Supermolecular Nanoentities of Vitamin B12 Derivative as a Link in the Evolution of the Parent Molecules During Self-Assembly at the Air-Water Interface

Nanoarchitectures with promising properties have now been formed from many important biomolecules. However, the preparation of nanoparticles of vitamin B₁₂ and its derivatives remains an ongoing research challenge. This paper describes the formation of supermolecular nanoentities (SMEs) of vitamin B₁₂ derivatives, unique nanoparticles with strong noncovalent intermolecular interactions, emerging properties, and activity. These were created by a nanoarchitectonic approach using directed assembly of layers at the air-water interface as a link in the chain of evolution of the parent molecules under specially created conditions. Such layers can be represented as a nanocosm, where, at a critical density, the assemblies act as nanoreactors in which the transformation of the original material occurs. The discovered SMEs not only replicate the functioning of vitamin B₁₂ assemblies with proteins in living organisms and act as vitamin B₁₂-depended enzymes but also demonstrate important advantages over vitamin B₁₂. They are more efficient in oxygen reduction/evolution reactions and in transformation into other forms. These SMEs, in performing advanced tasks, are an alternative to widely used materials based on noble metals for catalysis, medicine, and environment protection. Our findings open new perspectives both for the fabrication of novel SMEs of biomolecules and for a better understanding of the evolution of biomolecules in nature.

Non-Covalent Integration of a [FeFe]-Hydrogenase Mimic to Multiwalled Carbon Nanotubes for Electrocatalytic Hydrogen Evolution

Surface integration of molecular catalysts inspired from the active sites of hydrogenase enzymes represents a promising route towards developing noble metal-free and sustainable technologies for H2 production. Efficient and stable catalyst anchoring is a key aspect to enable this approach. Herein, we report the preparation and electrochemical characterization of an original diironhexacarbonyl complex including two pyrene groups per catalytic unit in order to allow for its smooth integration, through π-interactions, onto multiwalled carbon nanotube-based electrodes. In this configuration, the grafted catalyst could reach turnover numbers for H2 production (TONH2 ) of up to 4±2×103 within 20 h of bulk electrolysis, operating at neutral pH. Post operando analysis of catalyst functionalized electrodes revealed the degradation of the catalytic unit occurred via loss of the iron carbonyl units, while the anchoring groups and most part of the ligand remained attached onto multiwalled carbon nanotubes.

Tailoring of Active Sites from Single to Dual Atom Sites for Highly Efficient Electrocatalysis

Single atom catalysts (SACs) have been attracting extensive attention in electrocatalysis because of their unusual structure and extreme atom utilization, but the low metal loading and unified single site induced scaling relations may limit their activity and practical application. Tailoring of active sites at the atomic level is a sensible approach to break the existing limits in SACs. In this review, SACs were first discussed regarding carbon or non-carbon supports. Then, five tailoring strategies were elaborated toward improving the electrocatalytic activity of SACs, namely strain engineering, spin-state tuning engineering, axial functionalization engineering, ligand engineering, and porosity engineering, so as to optimize the electronic state of active sites, tune d orbitals of transition metals, adjust adsorption strength of intermediates, enhance electron transfer, and elevate mass transport efficiency. Afterward, from the angle of inducing electron redistribution and optimizing the adsorption nature of active centers, the synergistic effect from adjacent atoms and recent advances in tailoring strategies on active sites with binuclear configuration which include simple, homonuclear, and heteronuclear dual atom catalysts (DACs) were summarized. Finally, a summary and some perspectives for achieving efficient and sustainable electrocatalysis were presented based on tailoring strategies, design of active sites, and in situ characterization.

Novel (Pt-Ox )-(Co-Oy ) Nonbonding Active Structures on Defective Carbon from Oxygen-Rich Coal Tar Pitch for Efficient HER and ORR

Atomic-scale utilization and coordination structure of Pt electrocatalyst is extremely crucial to decrease loading mass and maximize activity for hydrogen evolution reactions (HERs) and oxygen reduction reactions (ORRs). A novel atomic-scale (Pt-O_x )-(Co-O_y ) nonbonding active structure is designed and constructed by anchoring Pt single atoms and Co atomic clusters on the defective carbon derived from oxygen-rich coal tar pitch (CTP). The Pt loading mass is extremely low and only 0.56 wt%. A new nonbonding interaction phenomenon between Pt-O_x and Co-O_y is found and confirmed based on X-ray absorption spectroscopy and density functional theory calculations. Based on the (Pt-O_x )-(Co-O_y ) nonbonding active structure, surface chemical field coupling with electrocatalysis for the HER and ORR is confirmed. It is found that the (Pt-O_x )-(Co-O_y ) nonbonding active structure exhibits high mass activities of 64.4 A cm^-2 mg_Pt ^-1 (at an overpotential of 100 mV) and 7.2 A cm^-2 mg_Pt ^-1 (at 0.8 V vs reversible hydrogen electrode) for the HER and ORR, respectively. The values are 6.5 and 11.6 times as much as those of commercial 20% Pt/C. The work provides innovative insight to design and understand efficient active sites of atomic-scale Pt on oxygen-rich CTP-derived carbon supports for electrocatalysis.

Probing the Synergistic Effects of Mg2+ on CO2 Reduction Reaction on CoPc by In Situ Electrochemical Scanning Tunneling Microscopy

We report herein the in situ electrochemical scanning tunneling microscopy (ECSTM) study on the synergistic effect of Mg²⁺ in CO₂ reduction reaction (CO₂RR) catalyzed by cobalt phthalocyanine (CoPc). ECSTM measurement molecularly resolves the self-assembled CoPc monolayer on the Au(111) substrate. In the CO₂ environment, high-contrast species are observed in the adlayer and assigned to the CO₂ adsorption on CoPc. Furthermore, the contrast of the CO₂-bound complex is higher in Mg²⁺-containing electrolytes than in Mg²⁺-free electrolytes, indicating the formation of the CoPc-CO₂-Mg²⁺ complex. The surface coverage of adsorbed CO₂ is positively correlated with the Mg²⁺ concentration as the additive in electrolytes up to a plateau of 30.8 ± 2.7% when c(Mg²⁺) > 30 mM. The potential step experiment indicates the higher CO₂ adsorption dynamics in Mg²⁺-containing electrolytes than without Mg²⁺. The rate constants of CO₂ adsorption and dissociation in different electrolytes are extracted from the data fitting of statistical results from in situ ECSTM experiments.

Metal-Corrole-Based Porous Organic Polymers for Electrocatalytic Oxygen Reduction and Evolution Reactions

Integrating molecular catalysts into designed frameworks often enables improved catalysis. Compared with porphyrin-based frameworks, metal-corrole-based frameworks have been rarely developed, although monomeric metal corroles are usually more efficient than porphyrin counterparts for the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). We herein report on metal-corrole-based porous organic polymers (POPs) as ORR and OER electrocatalysts. M-POPs (M=Mn, Fe, Co, Cu) were synthesized by coupling metal 10-phenyl-5,15-(4-iodophenyl)corrole with tetrakis(4-ethynylphenyl)methane. Compared with metal corrole monomers, M-POPs displayed significantly enhanced catalytic activity and stability. Co-POP outperformed other M-POPs by achieving four-electron ORR with a half-wave potential of 0.87 V vs. RHE and reaching 10 mA cm^-2 OER current density at 340 mV overpotential. This work is unparalleled to develop and explore metal-corrole-based POPs as electrocatalysts.

Electrocatalytic hydrogen generation using tripod containing pyrazolylborate-based copper(ii), nickel(ii), and iron(iii) complexes loaded on a glassy carbon electrode

Three transition metal complexes (MC) namely, [TpMeMeCuCl(H2O)] (CuC), [TpMeMeNiCl] (NiC), and [TpMeMeFeCl2(H2O)] (FeC) {TpMeMe = tris(3,5-dimethylpyrazolyl)borate} were synthesized and structurally characterized. The three complexes CuC, NiC, and FeC-modified glassy carbon (GC) were examined as molecular electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution (0.1 M KOH). Various GC-MC electrodes were prepared by loading different amounts (ca. 0.2-0.8 mg cm-2) of each metal complex on GC electrodes. These electrodes were used as cathodes in aqueous alkaline solutions (0.1 M KOH) to efficiently generate H2 employing various electrochemical techniques. The three metal complexes' HER catalytic activity was assessed using cathodic polarization studies. The charge-transfer kinetics of the HER at the (GC-MC)/OH- interface at a given overpotential were also studied using the electrochemical impedance spectroscopy (EIS) technique. The electrocatalyst's stability and long-term durability tests were performed employing cyclic voltammetry (repetitive cycling up to 5000 cycles) and 48 h of chronoamperometry measurements. The catalytic evolution of hydrogen on the three studied MC surfaces was further assessed using density functional theory (DFT) simulations. The GC-CuC catalysts revealed the highest HER electrocatalytic activity, which increased with the catalyst loading density. With a low HER onset potential (E HER) of -25 mV vs. RHE and a high exchange current density of 0.7 mA cm-2, the best performing electrocatalyst, GC-CuC (0.8 mg cm-2), showed significant HER catalytic performance. Furthermore, the best performing electrocatalyst required an overpotential value of 120 mV to generate a current density of 10 mA cm-2 and featured a Tafel slope value of -112 mV dec-1. These HER electrochemical kinetic parameters were comparable to those measured here for the commercial Pt/C under the same operating conditions (-10 mV vs. RHE, 0.88 mA cm-2, 108 mV dec-1, and 110 mV to yield a current density of 10 mA cm-2), as well as the most active molecular electrocatalysts for H2 generation from aqueous alkaline electrolytes. Density functional theory (DFT) simulations were used to investigate the nature of metal complex activities in relation to hydrogen adsorption. The molecular electrostatic surface potential (MESP) of the metal complexes was determined to assess the putative binding sites of the H atoms to the metal complex.

Multi-atom cluster catalysts for efficient electrocatalysis

This review presents recent developments in the synthesis, modulation and characterization of multi-atom cluster catalysts for electrochemical energy applications.

Ball-milling induced debonding of surface atoms from metal bulk for construing high-performance dual-site single-atom catalysts

Insert abstract text here. One of the most pressing challenges in single-atom catalysis is the manipulation of the coordination environment of the central metals to maximize catalyst performance. Herein, we fabricated a high-performance catalyst (Co-SNC) by introducing S into the neighboring position of the Co-N4 coordination. The developed ball-milling method enabled large-scale synthesis, and over 4.7 g of Co-SNC could be produced in one pot. In the benzylamine coupling reaction, Co-SNC exhibited the highest conversion of 97.5% with 99% selectivity toward N-benzylidenebenzylamine in 10 h among various Co catalysts. Density functional theory calculations revealed the crucial role of S atoms, which serve as the active sites for O2 activation, leaving the Co atoms free to adsorb benzylamine. Consequently, the adsorption energies of O2 and benzylamine were significantly increased. Our strategy suggests a feasible approach to enhance catalytic performance by delicately integrating dual active sites into a single catalyst unit.