Abstract Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A postulate is that iron-containing sites exist primarily a pyridinic Fe-N 4 ligation environment, yet, molecular model generally feature pyrrolic coordination. Herein, we report hexaazacyclophane macrocycle, (phen 2 N )Fe, compare its spectroscopic,...

A variety of next-generation energy processes utilize the electrochemical interconversions dioxygen and water as oxygen reduction reaction (ORR) evolution (OER). Reported here are first estimates standard potential O2 + 4e– 4H+ ⇋ 2H2O couple in organic solvents. The values +1.21 V acetonitrile (MeCN) +0.60 N,N-dimethylformamide (DMF), each versus ferrocenium/ferrocene (Fc+/0) respective solvent (as all potentials reported here). have been determined using a thermochemical cycle that combines...

Improved electrocatalysts for the oxygen reduction reaction (ORR) are critical advancement of fuel cell technologies. Herein, we report a series 11 soluble iron porphyrin ORR that possess turnover frequencies (TOFs) from 3 s-1 to an unprecedented value 2.2 × 106 s-1. These TOFs correlate with overpotential, which can be modulated by changing E1/2 catalyst using different ancillary ligands, solvent and solution acidity, catalyst's protonation state. The overpotential is well-defined these...

Several substituted iron-porphyrin complexes were evaluated for oxygen reduction reaction (ORR) electrocatalysis in different homogeneous and heterogeneous media. The selectivity four-electron to H2O versus two-electron H2O2 varies substantially from one medium another a given catalyst. In many cases, the influence of which catalyst is has larger effect on observed than factors attributable chemical modification For instance, introduction potential proton relays variable effects depending...

The catalytic reduction of O2 to H2O is important for energy transduction in both synthetic and natural systems. Herein, we report a kinetic thermochemical study the oxygen reaction (ORR) catalyzed by iron tetraphenylporphyrin (Fe(TPP)) N,N′-dimethylformamide using decamethylferrocene as soluble reductant para-toluenesulfonic acid (pTsOH) proton source. This work identifies characterizes intermediates their thermochemistry, providing detailed mechanistic understanding system. Specifically,...

A series of mononuclear pseudomacrocyclic cobalt complexes have been investigated as catalysts for O2 reduction. Each these complexes, with CoIII/II reduction potentials that span nearly 400 mV, mediate highly selective two-electron to H2O2 (93–99%) using decamethylferrocene (Fc*) the reductant and acetic acid proton source. Kinetic studies reveal rate exhibits a first-order dependence on [Co] [AcOH], but no [O2] or [Fc*]. linear correlation is observed between log(TOF) vs E1/2(CoIII/II)...

Facile and selective 4e–/4H+ electrochemical reduction of O2 to H2O in aqueous medium has been a sought-after goal for several decades. Elegant but synthetically demanding cytochrome c oxidase mimics have demonstrated is possible with rate constants as fast 105 M–1 s–1 under heterogeneous conditions media. Over the past few years, situ mechanistic investigations on iron porphyrin complexes adsorbed electrodes revealed that selectivity this multielectron multiproton process governed by...

We describe here a direct comparison of electrochemical and spectrochemical experiments to determine rates selectivity oxygen reduction catalyzed by iron 5,10,15,20-meso-tetraphenylporphyrin chloride. Good agreement was found between the two methods, suggesting same mechanism is occurring under both conditions, with third-order rate law, similar selectivity, derived constants agreeing within factor at most 4, k(cat) ≅ 2 × 10(6) M(-2) s(-1). This Communication provides rare example redox...

Improving molecular catalysis for important electrochemical proton-coupled electron transfer (PCET) reactions, such as the interconversions of H+/H2, O2/H2O, CO2/CO, and N2/NH3, is an ongoing challenge. Synthetic modifications to catalysts are valuable but often show trade-offs between turnover frequency (TOF) effective overpotential required initiate (ηeff). Herein, we derive a new approach improving efficiencies—higher TOF at lower ηeff—by changing concentrations properties reactants...

ConspectusThe oxygen reduction reaction (ORR) is a multiproton/multielectron transformation in which dioxygen (O2) reduced to water or hydrogen peroxide and serves as the cathode most fuel cells. The ORR (O2 + 4e– 4H+ → 2H2O) involves up nine substrates thus requires navigating complicated landscape, typically with several high-energy intermediates. Many catalysts can perform this reaction, though few operate fast rates at low overpotentials (close thermodynamic potential). Attempts optimize...

Tandem dye-sensitized photoelectrosynthesis cells are promising architectures for the production of solar fuels and commodity chemicals. A key bottleneck in development these is low efficiency photocathodes, leading to small current densities. Herein, we report a new design principle highly active photocathodes that relies on outer-sphere reduction substrate from dye, generating an unstable radical proceeds desired product. We show direct dioxygen nickel oxide (NiO) leads H2O2. In presence...

Proton-coupled electron-transfer (PCET) steps play a key role in energy conversion reactions. Molecular PCET reactions are well-described by "square schemes" which the overall thermochemistry of reaction is broken into its constituent proton-transfer and components. Although this description has been essential for understanding molecular PCET, no such framework exists that take place at electrode surfaces. Herein, we develop square scheme interfacial investigating electrochemistry...

Interfacial proton-coupled electron transfer (PCET) reactions are central to the operation of a wide array energy conversion technologies, but molecular-level insights into interfacial PCET limited. At carbon surfaces, designer sites for can be incorporated by conjugating organic acid functional groups graphite edges though aromatic phenazine linkages. these graphite-conjugated catalysts (GCCs) bearing moieties, is driven complex electrostatic and field gradients that difficult probe...

Detection of nitric oxide (NO) in biological systems is challenging due to both physicochemical properties NO and limitations current imaging modalities probes. Magnetic resonance (MRI) could be applied for studying living tissue with high spatiotemporal resolution, but there still a need chemical agents that effectively sensitize MRI production. To develop suitable probe, we studied the interactions between library manganese complexes various oxidation states molecular structures. Among...

The synthesis of a new tripodal ligand family that contains tertiary amine groups in the second-coordination sphere is reported. ligands are tris(amido)amine derivatives, with pendant amines attached via peptide coupling strategy. They were designed to function as molecular catalysts for oxygen reduction reaction (ORR), which acid/base group could improve catalyst performance. Two members each metalated cobalt(II) and zinc(II) afford trigonal-monopyramidal complexes. cobalt complexes...

Interfacial ET processes can be broadly classified as either outer-sphere or inner-sphere . For reactions, the electrode serves only a chemically inert source sink of electrons, whereas, for accompanies bond rearrangement at surface. While is well-described by Marcus-type models, there currently exists no analogous molecular-level understanding surfaces, despite central role these reactions in virtually all electrochemical technologies, ranging from supercapacitors to batteries fuel cells...