Unlocking the Potential for Methanol Synthesis via Electrochemical CO Reduction Using CoPc-Based Molecular Catalysts.

The electrochemical CO reduction reaction (CORR) to produce methanol (CHOH) is an attractive yet challenging approach due to a lack of selective electrocatalysts. An immobilized cobalt phthalocyanine (CoPc) molecular catalyst has emerged as a promising electrocatalyst for CHOH synthesis, demonstrating decent activity and selectivity through a CO-CO-CHOH cascade reaction. However, CoPc's performance is limited by its weak binding strength toward the CO intermediate.

The influence of exogenous amines on the electrochemical CO reduction activity of a cobalt-pyridyldiimine catalyst.

Studying the interactions between CO sorbents and electrocatalysts for the electrochemical CO reduction reaction (-CORR) can offer viable strategies to advance the development of the Reactive Capture of CO (RCC). In this report we studied the effect of amines on the performance of the [Co(PDI-Py)] catalyst for the -CORR. The presence of amines shifts the onset potential for the -CORR more positive and increases the catalytic activity while maintaining the high Faradaic efficiency (≥90%) for CO production.

Mitigating Cobalt Phthalocyanine Aggregation in Electrocatalyst Films through Codeposition with an Axially Coordinating Polymer.

Cobalt phthalocyanine (CoPc) is a promising molecular catalyst for aqueous electroreduction of CO, but its catalytic activity is limited by aggregation at high loadings. Codeposition of CoPc onto electrode surfaces with the coordinating polymer poly(4-vinylpyridine) (P4VP) mitigates aggregation in addition to providing other catalytic enhancements. Transmission and diffuse reflectance UV-vis measurements demonstrate that a combination of axial coordination and π-stacking effects from pyridyl moieties in P4VP serve to disperse cobalt phthalocyanine in deposition solutions and help prevent reaggregation in deposited films.

Selective Reduction of Aqueous Nitrate to Ammonium with an Electropolymerized Chromium Molecular Catalyst.

Nitrate (NO) is a common nitrogen-containing contaminant in agricultural, industrial, and low-level nuclear wastewater that causes significant environmental damage. In this work, we report a bioinspired Cr-based molecular catalyst incorporated into a redox polymer that selectively and efficiently reduces aqueous NO to ammonium (NH), a desirable value-added fertilizer component and industrial precursor, at rates of ∼0.36 mmol NH mg h with >90% Faradaic efficiency for NH.

Atomic Layer Deposition of Cu Electrocatalysts on Gas Diffusion Electrodes for CO Reduction.

Electrochemical reduction of CO using Cu catalysts enables the synthesis of C products including CH and CHOH. In this study, Cu catalysts were fabricated using plasma-enhanced atomic layer deposition (PEALD), achieving conformal deposition of catalysts throughout 3-D gas diffusion electrode (GDE) substrates while maintaining tunable control of Cu nanoparticle size and areal loading. The electrochemical CO reduction at the Cu surface yielded a total Faradaic efficiency (FE) > 75% for C products.

Translating Catalyst-Polymer Composites from Liquid to Gas-Fed CO Electrolysis: A CoPc-P4VP Case Study.

The electrochemical CO reduction reaction (CORR) in gas-fed flow electrolyzers using gas diffusion electrodes (GDEs) generates industrially relevant activities and provides a promising approach for carbon recycling. Developing effective catalyst systems on GDEs is critical for achieving high activities. Catalyst-polymer composites (CPCs) formed between immobilized molecular catalysts and coordinating polymers exhibit positive synergies for the enhancement of CORR activity.

Strategies for breaking molecular scaling relationships for the electrochemical CO reduction reaction.

The electrocatalytic CO reduction reaction (CORR) is a promising strategy for converting CO to fuels and value-added chemicals using renewable energy sources. Molecular electrocatalysts show promise for the selective conversion of CO to single products with catalytic activity that can be tuned through synthetic structure modifications. However, for the CORR by traditional molecular catalysts, beneficial decreases in overpotentials are usually correlated with detrimental decreases in catalytic activity.

Considering the Influence of Polymer-Catalyst Interactions on the Chemical Microenvironment of Electrocatalysts for the CO Reduction Reaction.

The electrochemical CO reduction reaction (CORR) is an attractive method for capturing intermittent renewable energy sources in chemical bonds, and converting waste CO into value-added products with a goal of carbon neutrality. Our group has focused on developing polymer-encapsulated molecular catalysts, specifically cobalt phthalocyanine (CoPc), as active and selective electrocatalysts for the CORR. When CoPc is adsorbed onto a carbon electrode and encapsulated in poly(4-vinylpyridine) (P4VP), its activity and reaction selectivity over the competitive hydrogen evolution reaction (HER) are enhanced by three synergistic effects: a primary axial coordination effect, a secondary reaction intermediate stabilization effect, and an outer-coordination proton transport effect.

Enhancing a Molecular Electrocatalyst's Activity for CO Reduction by Simultaneously Modulating Three Substituent Effects.

The electrocatalytic activity for CO reduction is greatly enhanced for Co complexes with pyridyldiimine-based ligands through the stepwise integration of three synergistic substituent effects: extended conjugation, electron-withdrawing ability, and intramolecular electrostatic effects. The stepwise incorporation of these effects into the catalyst structures results in a series of complexes that show an atypical inverse scaling relationship for CO reduction-the maximum activity of the resulting catalysts increases as the onset potentials are driven positive due to the ligand electronic substituent effects. Incorporating all three effects simultaneously into the catalyst structure results in a Co complex [Co(PDI-PyCHI)] with dramatically enhanced activity for CO reduction, operating with over an order of magnitude higher activity (TOF = 4.

A CoVO precatalyst for the oxygen evolution reaction: highlighting the importance of postmortem electrocatalyst characterization.

Vanadium-doped cobalt oxide materials have emerged as a promising class of catalysts for the oxygen evolution reaction. Previous studies suggest vanadium doping in crystalline Co spinel materials tunes the electronic structure and stabilizes surface intermediates. We report a CoV2O4 material that shows good activity for the oxygen evolution reaction.

Determining the coordination environment and electronic structure of polymer-encapsulated cobalt phthalocyanine under electrocatalytic CO reduction conditions using X-Ray absorption spectroscopy.

Encapsulating cobalt phthalocyanine (CoPc) within the coordinating polymer poly-4-vinylpyridine (P4VP) results in a catalyst-polymer composite (CoPc-P4VP) that selectively reduces CO2 to CO at fast rates at low overpotential. In previous studies, we postulated that the enhanced selectively for CO over H2 production within CoPc-P4VP compared to the parent CoPc complex is due to a combination of primary, secondary, and outer-coordination sphere effects imbued by the encapsulating polymer. In this work, we perform in situ electrochemical X-ray absorption spectroscopy measurements to study the oxidation state and coordination environment of Co as a function of applied potential for CoPc, CoPc-P4VP, and CoPc with an axially-coordinated py, CoPc(py).

Modulating the mechanism of electrocatalytic CO reduction by cobalt phthalocyanine through polymer coordination and encapsulation.

The selective and efficient electrochemical reduction of CO to single products is crucial for solar fuels development. Encapsulating molecular catalysts such as cobalt phthalocyanine within coordination polymers such as poly-4-vinylpyridine leads to dramatically increased activity and selectivity for CO reduction. In this study, we use a combination of kinetic isotope effect and proton inventory studies to explain the observed increase in activity and selectivity upon polymer encapsulation.

Imidazole for Pyridine Substitution Leads to Enhanced Activity Under Milder Conditions in Cobalt Water Oxidation Electrocatalysis.

A previously reported cobalt complex featuring a tetraimidazolyl-substituted pyridine chelate is an active water oxidation electrocatalyst with moderate overpotential at pH 7. While this complex decomposes rapidly to a less-active species under electrocatalytic conditions, detailed electrochemical studies support the agency of an initial molecular catalyst. Cyclic voltammetry measurements confirm that the imidazolyl donors result in a more electron-rich Co center when compared with previous pyridine-based systems.

Electrocatalytic CO reduction by a cobalt bis(pyridylmonoimine) complex: effect of acid concentration on catalyst activity and stability.

A Co complex with a redox-active bis(pyridylmonoimine) ligand has been prepared and shows catalytic activity for electrochemical CO reduction in acetonitrile. Addition of a proton source such as water or trifluoroethanol dramatically improves the activity and stability of the molecular catalyst. The Co complex reduces CO to CO selectively at -1.

Gastight Hydrodynamic Electrochemistry: Design for a Hermetically Sealed Rotating Disk Electrode Cell.

Rotating disk electrodes (RDEs) are widely used in electrochemical characterization to analyze the mechanisms of various electrocatalytic reactions. RDE experiments often make use of or require collection and quantification of gaseous products. The combination of rotating parts and gaseous analytes makes the design of RDE cells that allow for headspace analysis challenging due to gas leaks at the interface of the cell body and the rotator.

Molecular Mixed-Metal Manganese Oxido Cubanes as Precursors to Heterogeneous Oxygen Evolution Catalysts.

Well-defined mixed-metal [CoMn3 O4 ] and [NiMn3 O4 ] cubane complexes were synthesized and used as precursors for heterogeneous oxygen evolution reaction (OER) electrocatalysts. The discrete clusters were dropcasted onto glassy carbon (GC) and indium tin oxide (ITO) electrodes, and the OER activities of the resulting films were evaluated. The catalytic surfaces were analyzed by various techniques to gain insight into the structure-function relationships of the electrocatalysts' heterometallic composition.

Tuning complex transition metal hydroxide nanostructures as active catalysts for water oxidation by a laser-chemical route.

Diverse transition metal hydroxide nanostructures were synthesized by laser-induced hydrolysis in a liquid precursor solution for alkaline oxygen evolution reaction (OER). Several active OER catalysts with fine control of composition, structure, and valence state were obtained including (Lix)[Ni0.66Mn0.

Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices.

Objective comparisons of electrocatalyst activity and stability using standard methods under identical conditions are necessary to evaluate the viability of existing electrocatalysts for integration into solar-fuel devices as well as to help inform the development of new catalytic systems. Herein, we use a standard protocol as a primary screen for evaluating the activity, short-term (2 h) stability, and electrochemically active surface area (ECSA) of 18 electrocatalysts for the hydrogen evolution reaction (HER) and 26 electrocatalysts for the oxygen evolution reaction (OER) under conditions relevant to an integrated solar water-splitting device in aqueous acidic or alkaline solution. Our primary figure of merit is the overpotential necessary to achieve a magnitude current density of 10 mA cm(-2) per geometric area, the approximate current density expected for a 10% efficient solar-to-fuels conversion device under 1 sun illumination.

A 10(6)-fold enhancement in N2-binding affinity of an Fe2(μ-H)2 core upon reduction to a mixed-valence Fe(II)Fe(I) state.

Transient hydride ligands bridging two or more iron centers purportedly accumulate on the iron-molybdenum cofactor (FeMoco) of nitrogenase, and their role in the reduction of N2 to NH3 is unknown. One role of these ligands may be to facilitate N2 coordination at an iron site of FeMoco. Herein, we consider this hypothesis and describe the preparation of a series of diiron complexes supported by two bridging hydride ligands.

Redox active iron nitrosyl units in proton reduction electrocatalysis.

Base metal, molecular catalysts for the fundamental process of conversion of protons and electrons to dihydrogen, remain a substantial synthetic goal related to a sustainable energy future. Here we report a diiron complex with bridging thiolates in the butterfly shape of the 2Fe2S core of the [FeFe]-hydrogenase active site but with nitrosyl rather than carbonyl or cyanide ligands. This binuclear [(NO)Fe(N2S2)Fe(NO)2](+) complex maintains structural integrity in two redox levels; it consists of a (N2S2)Fe(NO) complex (N2S2=N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane) that serves as redox active metallodithiolato bidentate ligand to a redox active dinitrosyl iron unit, Fe(NO)2.

Studies of cobalt-mediated electrocatalytic CO2 reduction using a redox-active ligand.

The cobalt complex [Co(III)N4H(Br)2](+) (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7),2,11,13,15-pentaene) was used for electrocatalytic CO2 reduction in wet MeCN with a glassy carbon working electrode.

Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction.

Objective evaluation of the activity of electrocatalysts for water oxidation is of fundamental importance for the development of promising energy conversion technologies including integrated solar water-splitting devices, water electrolyzers, and Li-air batteries. However, current methods employed to evaluate oxygen-evolving catalysts are not standardized, making it difficult to compare the activity and stability of these materials. We report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts.

Electrooxidation of alcohols catalyzed by amino alcohol ligated ruthenium complexes.

Ruthenium transfer hydrogenation catalysts physisorbed onto edge-plane graphite electrodes are active electrocatalysts for the oxidation of alcohols. Electrooxidation of CH3OH (1.23 M) in a buffered aqueous solution at pH 11.

Electrocatalytic hydrogen evolution in acidic water with molecular cobalt tetraazamacrocycles.

A series of water-soluble molecular cobalt complexes of tetraazamacrocyclic ligands are reported for the electrocatalytic production of H(2) from pH 2.2 aqueous solutions. The comparative data reported for this family of complexes shed light on their relative efficiencies for hydrogen evolution in water.

Electrocatalytic O2 reduction by covalently immobilized mononuclear copper(I) complexes: evidence for a binuclear Cu2O2 intermediate.

A Cu(I) complex of 3-ethynyl-phenanthroline covalently immobilized onto an azide-modified glassy carbon surface is an active electrocatalyst for the four-electron (4-e) reduction of O(2) to H(2)O. The rate of O(2) reduction is second-order in Cu coverage at moderate overpotential, suggesting that two Cu(I) species are necessary for efficient 4-e reduction of O(2). Mechanisms for O(2) reduction are proposed that are consistent with the observations for this covalently immobilized system and previously reported results for a similar physisorbed Cu(I) system.