Designing neighboring-site activation of single atom via tunnel ions for boosting acidic oxygen evolution.

Realizing an efficient turnover frequency in the acidic oxygen evolution reaction by modifying the reaction configuration is crucial in designing high-performance single-atom catalysts. Here, we report a "single atom-double site" concept, which involves an activatable inert manganese atom redox chemistry in a single-atom Ru-Mn dual-site platform with tunnel Ni ions as the trigger. In contrast to conventional single-atom catalysts, the proposed configuration allows direct intramolecular oxygen coupling driven by the Ni ions intercalation effect, bypassing the secondary deprotonation step instead of the kinetically sluggish adsorbate evolution mechanism. The strong bonding of Ni ions activates the inert manganese terminal groups and inhibits the cross-site disproportionation process inherent in the Mn scaffolding, which is crucial to ensure the dual-site platform. As a result, the single-atom Ru-Ni-Mn octahedral molecular sieves catalyst delivers a low overpotential, adequate mass activity and good stability.

Modulating Spin of Atomic Manganese Center for High-Performance Oxygen Reduction Reaction.

Single atom catalysts (SACs) are promising non-precious catalysts for oxygen reduction reaction (ORR). Unfortunately, the ORR SACs usually suffer from unsatisfactory activity and in particular poor stability. Herein, we report atomically dispersed manganese (Mn) embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for ORR in alkaline electrolyte, realizing a half-wave potential (E1/2) of 0.883 V vs. reversible hydrogen electrode (RHE) with negligible activity degradation after 40,000 cyclic voltammetry (CV) cycles in 0.1 M KOH. Introducing sulfur (S) to form Mn-S coordination changes the spin state of single Mn atom from high-spin to low-spin, verified by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements as well as density functional theory (DFT) calculations, which effectively optimizes the oxygen intermediates adsorption over the single Mn atomic sites and thus greatly improves the ORR activity.

Accelerated Proton Transfer in Asymmetric Active Units for Sustainable Acidic Oxygen Evolution Reaction.

The poor durability of Ru-based catalysts limits the practical application in proton exchange membrane water electrolysis (PEMWE). Here, we report that the asymmetric active units in Ru1-xMxO2 (M = Sb, In, and Sn) binary solid solution oxides are constructed by introducing acid-resistant p-block metal sites, breaking the activity and stability limitations of RuO2 in acidic oxygen evolution reaction (OER). Constructing highly asymmetric Ru-O-Sb units with a strong electron delocalization effect significantly shortens the spatial distance between Ru and Sb sites, improving the bonding strength of the overall structure. The unique two-electron redox couples at Sb sites in asymmetric active units trigger additional chemical steps at different OER stages, facilitating continuous proton transfer. The optimized Ru0.8Sb0.2O2 solid solution requires a superlow overpotential of 160 mV at 10 mA cm-2 and a record-breaking stability of 1100 h in an acidic electrolyte. Notably, the scale-prepared Ru0.8Sb0.2O2 achieves efficient PEMWE performance under industrial conditions. General mechanism analysis shows that the enhanced proton transport in the asymmetric Ru-O-M unit provides a new working pathway for acidic OER, breaking the scaling relationship without sacrificing stability.

Incorporation of Pd Single-Atom Sites in Perovskite with an Excellent Selectivity toward Photocatalytic Semihydrogenation of Alkynes.

Semihydrogenation is a crucial industrial process. Noble metals such as Pd have been extensively studied in semihydrogenation reactions, owing to their unique catalytic activity toward hydrogen activation. However, the overhydrogenation of alkenes to alkanes often happens due to the rather strong adsorption of alkenes on Pd active phases. Herein, we demonstrate that the incorporation of Pd active phases as single-atom sites in perovskite lattices such as SrTiO3 can greatly alternate the electronic structure and coordination environment of Pd active phases to facilitate the desorption of alkenes rather than further hydrogenation. Furthermore, the incorporated Pd sites can be well stabilized without sintering by a strong host-guest interaction with SrTiO3 during the activation of H species in hydrogenation reactions. As a result, the Pd incorporated SrTiO3 (Pd-SrTiO3) exhibits an excellent time-independent selectivity (>99.9 %) and robust durability for the photocatalytic semihydrogenation of phenylacetylene to styrene. This strategy based on incorporation of active phases in perovskite lattices will have broad implications in the development of high-performance photocatalysts for selective hydrogenation reactions.

A catalyst family of high-entropy alloy atomic layers with square atomic arrangements comprising iron- and platinum-group metals.

We report a catalyst family of high-entropy alloy (HEA) atomic layers having three elements from iron-group metals (IGMs) and two elements from platinum-group metals (PGMs). Ten distinct quinary compositions of IGM-PGM-HEA with precisely controlled square atomic arrangements are used to explore their impact on hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The PtRuFeCoNi atomic layers perform enhanced catalytic activity and durability toward HER and HOR when benchmarked against the other IGM-PGM-HEA and commercial Pt/C catalysts. Operando synchrotron x-ray absorption spectroscopy and density functional theory simulations confirm the cocktail effect arising from the multielement composition. This effect optimizes hydrogen-adsorption free energy and contributes to the remarkable catalytic activity observed in PtRuFeCoNi. In situ electron microscopy captures the phase transformation of metastable PtRuFeCoNi during the annealing process. They transform from random atomic mixing (25°C), to ordered L10 (300°C) and L12 (400°C) intermetallic, and finally phase-separated states (500°C).

Enhanced Carbon-Carbon Coupling at Interfaces with Abrupt Coordination Number Changes.

Cu-catalyzed electrochemical CO2 reduction reaction (CO2RR) produces multi-carbon (C2+) chemicals with considerable selectivities and activities, yet required high overpotentials impede its practical application. Here, we design interfaces with abrupt coordination number (CN) changes that greatly reduce the applied potential for achieving high C2+ Faradaic efficiency (FE). Encouraged by the mechanistic finding that the coupling between *CO and *CO(H) is the most probable C-C bond formation path, we use Cu2O- and Cu-phthalocyanine-derived Cu (OD-Cu and PD-Cu) to build the interface. Using operando X-ray absorption spectroscopy (XAS), we find that the Cu CN of OD-Cu is ~11, favoring CO* adsorption, while the PD-Cu has a COH*-favorable CN of ~4. Operando Raman spectroscopy revealed that the interfaces with abrupt CN changes promote *OCCOH formation. As a result, the designed catalyst achieves a C2+ FE of 85±2 % at 220 mA cm-2 in a zero-gap CO2 electrolyzer. An improvement of C2+ FE by 3 times is confirmed at the low potential regime where the current density is 60-140 mA cm-2, compared to bare OD-Cu. We report a 45-h stable CO2RR operation at 220 mA cm-2, producing a C2+ product FE of ~80 %.

Dynamic chloride ion adsorption on single iridium atom boosts seawater oxidation catalysis.

Seawater electrolysis offers a renewable, scalable, and economic means for green hydrogen production. However, anode corrosion by Cl- pose great challenges for its commercialization. Herein, different from conventional catalysts designed to repel Cl- adsorption, we develop an atomic Ir catalyst on cobalt iron layered double hydroxide (Ir/CoFe-LDH) to tailor Cl- adsorption and modulate the electronic structure of the Ir active center, thereby establishing a unique Ir-OH/Cl coordination for alkaline seawater electrolysis. Operando characterizations and theoretical calculations unveil the pivotal role of this coordination state to lower OER activation energy by a factor of 1.93. The Ir/CoFe-LDH exhibits a remarkable oxygen evolution reaction activity (202 mV overpotential and TOF = 7.46 O2 s-1) in 6 M NaOH+2.8 M NaCl, superior over Cl--free 6 M NaOH electrolyte (236 mV overpotential and TOF = 1.05 O2 s-1), with 100% catalytic selectivity and stability at high current densities (400-800 mA cm-2) for more than 1,000 h.

Constructing regulable supports via non-stoichiometric engineering to stabilize ruthenium nanoparticles for enhanced pH-universal water splitting.

Establishing appropriate metal-support interactions is imperative for acquiring efficient and corrosion-resistant catalysts for water splitting. Herein, the interaction mechanism between Ru nanoparticles and a series of titanium oxides, including TiO, Ti4O7 and TiO2, designed via facile non-stoichiometric engineering is systematically studied. Ti4O7, with the unique band structure, high conductivity and chemical stability, endows with ingenious metal-support interaction through interfacial Ti-O-Ru units, which stabilizes Ru species during OER and triggers hydrogen spillover to accelerate HER kinetics. As expected, Ru/Ti4O7 displays ultralow overpotentials of 8 mV and 150 mV for HER and OER with a long operation of 500 h at 10 mA cm-2 in acidic media, which is expanded in pH-universal environments. Benefitting from the excellent bifunctional performance, the proton exchange membrane and anion exchange membrane electrolyzer assembled with Ru/Ti4O7 achieves superior performance and robust operation. The work paves the way for efficient energy conversion devices.

Polarized Ultrathin BN Induced Dynamic Electron Interactions for Enhancing Acidic Oxygen Evolution.

Developing ruthenium-based heterogeneous catalysts with an efficient and stable interface is essential for enhanced acidic oxygen evolution reaction (OER). Herein, we report a defect-rich ultrathin boron nitride nanosheet support with relatively independent electron donor and acceptor sites, which serves as an electron reservoir and receiving station for RuO2, realizing the rapid supply and reception of electrons. Through precisely controlling the reaction interface, a low OER overpotential of only 180 mV (at 10 mA cm-2) and long-term operational stability (350 h) are achieved, suggesting potential practical applications. In situ characterization and theoretical calculations have validated the existence of a localized electronic recycling between RuO2 and ultrathin BN nanosheets (BNNS). The electron-rich Ru sites accelerate the adsorption of water molecules and the dissociation of intermediates, while the interconnection between the O-terminal and B-terminal edge establishes electronic back-donation, effectively suppressing the over-oxidation of lattice oxygen. This study provides a new perspective for constructing a stable and highly active catalytic interface.

Bipyridine-Confined Silver Single-Atom Catalysts Facilitate In-Plane C-O Coupling for Propylene Electrooxidation.

The electrooxidation of propylene presents a promising route for the production of 1,2-propylene glycol (PG) under ambient conditions. However, the C-O coupling process remains a challenge owing to the high energy barrier. In this work, we developed a highly efficient electrocatalyst of bipyridine-confined Ag single atoms on UiO-bpy substrates (Ag SAs/UiO-bpy), which exposed two in-plane coordination vacancies during reaction for the co-adsorption of key intermediates. Detailed structure and electronic property analyses demonstrate that CH3CHCH2OH* and *OH could stably co-adsorb in a square planar configuration, which then accelerates the charge transfer between them. The combination of stable co-adsorption and efficient charge transfer facilitates the C-O coupling process, thus significantly lowering its energy barrier. At 2.4 V versus a reversible hydrogen electrode, Ag SAs/UiO-bpy achieved a record-high activity of 61.9 gPG m-2 h-1. Our work not only presents a robust electrocatalyst but also advances a new perspective on catalyst design for propylene electrooxidation.

Direct Electrosynthesis of Metal Nanoparticles on Ti3C2Tx-Mxene during Hydrogen Evolution.

Herein, we propose a simple yet effective method to deposit metal nanoparticles on Ti3C2Tx-MXene via direct electrosynthesis. Without using any reducing reagent or annealing under reducing atmosphere, it allows the conversion of metal salts (e.g., PtCl4, RuCl3·yH2O, IrCl3·zH2O, AgNO3, and CuCl2·2H2O) to metal nanoparticles with a small particle size (ca. 2 nm). Under these circumstances, it was realized that the support effect from Ti3C2Tx-MXene (electron pushing) is quite profound, in which the Ti3C2Tx-MXene support will act as an electron donor to push the electron to Pt nanoparticles and increase the electron density of Pt nanoparticles. It populates the antibonding state of Pt-Pt bonds as well as the adsorbate level that leads to a "weakening" of the ΔGH* in the optimal position. This rationalizes the outstanding activity of Pt/Ti3C2Tx-MXene (5 wt %, η10 = 16 mV) for the hydrogen evolution reaction (HER). In addition, this direct electrosynthesis method grants the growth of two or multiple types of metal nanoparticles on the Ti3C2Tx-MXene substrate that can perform dual or multiple functions as desired. For instance, one can prepare an electrocatalyst with Pt (2.5 wt %) and Ru nanoparticles (2.5 wt %) on the Ti3C2Tx-MXene support from the same synthetic method. This electrocatalyst (Pt_Ru/Ti3C2Tx-MXene) can display good electrocatalytic HER performance in both acid (0.5 M H2SO4) and alkaline electrolytes (1.0 M KOH).

Switching the Oxygen Evolution Mechanism on Atomically Dispersed Ru for Enhanced Acidic Reaction Kinetics.

Designing stable single-atom electrocatalysts with lower energy barriers is urgent for the acidic oxygen evolution reaction. In particular, the atomic catalysts are highly dependent on the kinetically sluggish acid-base mechanism, limiting the reaction paths of intermediates. Herein, we successfully manipulate the steric localization of Ru single atoms at the Co3O4 surface to improve acidic oxygen evolution by precise control of the anchor sites. The delicate structure design can switch the reaction mechanism from the lattice oxygen mechanism (LOM) to the optimized adsorbate evolution mechanism (AEM). In particular, Ru atoms embedded into cation vacancies reveal an optimized mechanism that activates the proton donor-acceptor function (PDAM), demonstrating a new single-atom catalytic pathway to circumvent the classic scaling relationship. Steric interactions with intermediates at the anchored Ru-O-Co interface played a primary role in optimizing the intermediates' conformation and reducing the energy barrier. As a comparison, Ru atoms confined to the surface sites exhibit a lattice oxygen mechanism for the oxygen evolution process. As a result, the delicate atom control of the spatial position presents a 100-fold increase in mass activity from 36.96 A gRu(ads)-1 to 4012.11 A gRu(anc)-1 at 1.50 V. These findings offer new insights into the precise control of single-atom catalytic behavior.

Operando Mössbauer Spectroscopic Tracking the Metastable State of Atomically Dispersed Tin in Copper Oxide for Selective CO2 Electroreduction.

Metastable state is the most active catalyst state that dictates the overall catalytic performance and rules of catalytic behaviors; however, identification and stabilization of the metastable state of catalyst are still highly challenging due to the continuous evolution of catalytic sites during the reaction process. In this work, operando 119Sn Mössbauer measurements and theoretical simulations were performed to track and identify the metastable state of single-atom Sn in copper oxide (Sn1-CuO) for highly selective CO2 electroreduction to CO. A maximum CO Faradaic efficiency of around 98% at -0.8 V (vs. RHE) over Sn1-CuO was achieved at an optimized Sn loading of 5.25 wt. %. Operando Mössbauer spectroscopy clearly identified the dynamic evolution of atomically dispersed Sn4+ sites in the CuO matrix that enabled the in situ transformation of Sn4+-O4-Cu2+ to a metastable state Sn4+-O3-Cu+ under CO2RR conditions. In combination with quasi in situ X-ray photoelectron spectroscopy, operando Raman and attenuated total reflectance surface enhanced infrared absorption spectroscopies, the promoted desorption of *CO over the Sn4+-O3 stabilized adjacent Cu+ site was evidenced. In addition, density functional theory calculations further verified that the in situ construction of Sn4+-O3-Cu+ as the true catalytic site altered the reaction path via modifying the adsorption configuration of the *COOH intermediate, which effectively reduced the reaction free energy required for the hydrogenation of CO2 and the desorption of the *CO, thereby greatly facilitating the CO2-to-CO conversion. This work provides a fundamental insight into the role of single Sn atoms on in situ tuning the electronic structure of Cu-based catalysts, which may pave the way for the development of efficient catalysts for high-selectivity CO2 electroreduction.

Valence Oscillation of Ru Active Sites for Efficient and Robust Acidic Water Oxidation.

The continuous oxidation and leachability of active sites in Ru-based catalysts hinder practical application in proton-exchange membrane water electrolyzers (PEMWE). Herein, robust inter-doped tungsten-ruthenium oxide heterostructures [(Ru-W)Ox ] fabricated by sequential rapid oxidation and metal thermomigration processes are proposed to enhance the activity and stability of acidic oxygen evolution reaction (OER). The introduction of high-valent W species induces the valence oscillation of the Ru sites during OER, facilitating the cyclic transition of the active metal oxidation states and maintaining the continuous operation of the active sites. The preferential oxidation of W species and electronic gain of Ru sites in the inter-doped heterostructure significantly stabilize RuOx on WOx substrates beyond the Pourbaix stability limit of bare RuO2 . Furthermore, the asymmetric Ru-O-W active units are generated around the heterostructure interface to adsorb the oxygen intermediates synergistically, enhancing the intrinsic OER activity. Consequently, the inter-doped (Ru-W)Ox heterostructures not only demonstrate an overpotential of 170 mV at 10 mA cm-2 and excellent stability of 300 h in acidic electrolytes but also exhibit the potential for practical applications, as evidenced by the stable operation at 0.5 A cm-2 for 300 h in PEMWE.

Boosting the Proton-coupled Electron Transfer via Fe-P Atomic Pair for Enhanced Electrochemical CO2 Reduction.

Single-atom catalysts exhibit superior CO2 -to-CO catalytic activity, but poor kinetics of proton-coupled electron transfer (PCET) steps still limit the overall performance toward the industrial scale. Here, we constructed a Fe-P atom paired catalyst onto nitrogen doped graphitic layer (Fe1 /PNG) to accelerate PCET step. Fe1 /PNG delivers an industrial CO current of 1 A with FECO over 90 % at 2.5 V in a membrane-electrode assembly, overperforming the CO current of Fe1 /NG by more than 300 %. We also decrypted the synergistic effects of the P atom in the Fe-P atom pair using operando techniques and density functional theory, revealing that the P atom provides additional adsorption sites for accelerating water dissociation, boosting the hydrogenation of CO2 , and enhancing the activity of CO2 reduction. This atom-pair catalytic strategy can modulate multiple reactants and intermediates to break through the inherent limitations of single-atom catalysts.

Boosting the Ultrastable High-Na-Content P2-type Layered Cathode Materials with Zero-Strain Cation Storage via a Lithium Dual-Site Substitution Approach.

P2-type layered transition-metal (TM) oxides, NaxTMO2, are highly promising as cathode materials for sodium-ion batteries (SIBs) due to their excellent rate capability and affordability. However, P2-type NaxTMO2 is afflicted by issues such as Na+/vacancy ordering and multiple phase transitions during Na-extraction/insertion, leading to staircase-like voltage profiles. In this study, we employ a combination of high Na content and Li dual-site substitution strategies to enhance the structural stability of a P2-type layered oxide (Na0.80Li0.024[Li0.065Ni0.22Mn0.66]O2). The experimental results reveal that these approaches facilitate the oxidation of Mn ions to a higher valence state, thereby affecting the local environment of both TM and Na ions. The resulting modification in the local structure significantly improves the Na-ion storage capabilities as required for cathode materials in SIBs. Furthermore, it induces a solid-solution reaction and enables nearly zero-strain operation (ΔV = 0.7%) in the Na0.80Li0.024[Li0.065Ni0.22Mn0.66]O2 cathode during cycling. The assembled full cells demonstrate an exceptional rate performance, with a retention rate of 87% at 10 C compared to that of 0.1 C, as well as an ultrastable cycling capability, maintaining a capacity retention of 73% at 2 C after 1000 cycles. These findings offer valuable insights into the electronic and structural chemistry of ultrastable cathode materials with "zero-strain" Na-ion storage.

Boosting photocatalytic hydrogen peroxide production by regulating electronic configuration of single Sb atoms via carbon vacancies in carbon nitrides.

Single-atom catalysts supported on semiconductors can serve as active sites for efficient oxygen reduction to hydrogen peroxide (H2O2). However, researchers have long been puzzled by the lack of guidance on optimizing the performance of single-atom photocatalysts. In this study, we propose a versatile strategy that utilizes carbon vacancies to regulate the electronic configuration of antimony (Sb) atoms on carbon nitrides (C3N4). This strategy has been found to significantly enhance the photocatalytic production of H2O2. The H2O2 evolution rate of Sb single-atom on carbon vacancy-rich C3N4 (designated as Sb1/Cv-C3N4) is 5.369 mmol g-1h-1, which is 10.9 times higher than C3N4 alone. By combining experimental characterizations and density functional theory simulations, we reveal the strong electronic interaction between Sb atoms and carbon vacancy-rich C3N4. This interaction is capable for maintaining the electron-rich state of Sb atoms, facilitating efficient electron transfer to pauling-type absorbed oxygen, and ultimately enhancing the formation of *OOH intermediates. This innovative defect-engineering approach can manipulate the electronic configuration of single-atom catalysts, providing a new avenue to boost the photocatalytic oxygen reduction reaction towards H2O2 production.

Dealloying-Induced Zeolite-like Metal Framework of AB2 Laves Phase Intermetallic Electrocatalysts.

Exploring an efficient and robust electrocatalyst for hydrogen evolution reaction (HER) at high pH and temperature holds the key to the industrial application of alkaline water electrolysis (AWE). Herein, we design an open tunnel structure by dealloying a series of Laves phase intermetallics, i.e., MCo2 and MRu0.25Co1.75 (M = Sc and Zr). The dealloying process can induce a zeolite-like metal framework for ScCo2 and ScRu0.25Co1.75 by stripping Sc metal from the center of a tunnel structure. This structural engineering significantly lowers their overpotentials at a current density of 500 mA/cm2 (η500) ca. 80 mV in 1.0 M KOH. Through a simple process, ScRu0.25Co1.75 can be easily decorated on a carbon cloth substrate and only requires 132 mV to reach 500 mA/cm2. More importantly it can maintain activity over 1000 h in industrial conditions (6.0 M KOH at 333 K), showing its potential for practical industrial applications.

Nanograin-Boundary-Abundant Cu2O-Cu Nanocubes with High C2+ Selectivity and Good Stability during Electrochemical CO2 Reduction at a Current Density of 500 mA/cm2.

Surface and interface engineering, especially the creation of abundant Cu0/Cu+ interfaces and nanograin boundaries, is known to facilitate C2+ production during electrochemical CO2 reductions over copper-based catalysts. However, precisely controlling the favorable nanograin boundaries with surface structures (e.g., Cu(100) facets and Cu[n(100)×(110)] step sites) and simultaneously stabilizing Cu0/Cu+ interfaces is challenging, since Cu+ species are highly susceptible to be reduced into bulk metallic Cu at high current densities. Thus, an in-depth understanding of the structure evolution of the Cu-based catalysts under realistic CO2RR conditions is imperative, including the formation and stabilization of nanograin boundaries and Cu0/Cu+ interfaces. Herein we demonstrate that the well-controlled thermal reduction of Cu2O nanocubes under a CO atmosphere yields a remarkably stable Cu2O-Cu nanocube hybrid catalyst (Cu2O(CO)) possessing a high density of Cu0/Cu+ interfaces, abundant nanograin boundaries with Cu(100) facets, and Cu[n(100)×(110)] step sites. The Cu2O(CO) electrocatalyst delivered a high C2+ Faradaic efficiency of 77.4% (56.6% for ethylene) during the CO2RR under an industrial current density of 500 mA/cm2. Spectroscopic characterizations and morphological evolution studies, together with in situ time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies, established that the morphology and Cu0/Cu+ interfacial sites in the as-prepared Cu2O(CO) catalyst were preserved under high polarization and high current densities due to the nanograin-boundary-abundant structure. Furthermore, the abundant Cu0/Cu+ interfacial sites on the Cu2O(CO) catalyst acted to increase the *CO adsorption density, thereby increasing the opportunity for C-C coupling reactions, leading to a high C2+ selectivity.

In-situ spectroscopic probe of the intrinsic structure feature of single-atom center in electrochemical CO/CO2 reduction to methanol.

While exploring the process of CO/CO2 electroreduction (COxRR) is of great significance to achieve carbon recycling, deciphering reaction mechanisms so as to further design catalytic systems able to overcome sluggish kinetics remains challenging. In this work, a model single-Co-atom catalyst with well-defined coordination structure is developed and employed as a platform to unravel the underlying reaction mechanism of COxRR. The as-prepared single-Co-atom catalyst exhibits a maximum methanol Faradaic efficiency as high as 65% at 30 mA/cm2 in a membrane electrode assembly electrolyzer, while on the contrary, the reduction pathway of CO2 to methanol is strongly decreased in CO2RR. In-situ X-ray absorption and Fourier-transform infrared spectroscopies point to a different adsorption configuration of *CO intermediate in CORR as compared to that in CO2RR, with a weaker stretching vibration of the C-O bond in the former case. Theoretical calculations further evidence the low energy barrier for the formation of a H-CoPc-CO- species, which is a critical factor in promoting the electrochemical reduction of CO to methanol.