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Electrochemical CO2 reduction to valuable chemicals represents a greenand sustainable approach to close the anthropogenic carbon cycle, but hasbeen impeded by low efficiency and high cost of electrocatalysts. Here, acost-effective hybrid catalyst consisting of hemin (chloroprotoporphyrin IXiron(III)), a product recovered from bovine blood, adsorbed onto commercialVulcan carbon is reported. Upon heat treatment, this material shows significantlyimproved activity and selectivity for CO2 reduction in water whileexhibiting good stability for more than 10 h. The heat treatment leads toconsecutive removal of the axial chlorine atom and decomposition of the ironporphyrin ring, restructuring to form atomic Fe sites. The optimized hybridcatalyst obtained at 900 °C shows near-unity selectivity for reduction of CO2to CO at a small overpotential of 310 mV. The insight into transformation ofadsorbed Fe complexes into single Fe atoms upon heat treatment providesguidance for development of single atom catalysts.

Herein we describe the synthesis and photophysical and electrochemical characterization of pyrimidopteridine-based photoredox catalysts. The pyrimidopteridines can be obtained from the corresponding N-oxides through photo-mediated oxygen atom transfer to a sacrificial acceptor molecule on gramscale. The presence of a triplet excited state was evidenced by means of transient absorption spectroscopy. Pyrimidopteridines are potent excited state oxidants with excited state reduction potentials exceeding +2.10 V vs. SCE in MeCN. The catalytic activity is illustrated in the photo-mediated oxidative annulation of 2-phenylbenzoic acid.

The direct electrochemistry of a HRP–chi–[C 4 mim][BF 4 ] film (where HRP = horseradish peroxidase, chi = chitosan, and [C 4 mim][BF 4 ] = the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate) has been studied by cyclic voltammetry on a glassy carbon electrode. The mechanism for the electrochemical reaction of HRP is suggested to be EC for the reduction, and CE for the following re-oxidation, as the oxidative peak potential remained approximately unchanged across the scan rate range. The half wave potential of HRP reduction was found to be pH dependent, suggesting that a concomitant proton and electron transfer is occurring. Using theoretical simulations of the experimentally obtained peak positions, the standard electron transfer rate constant, k 0 , was found to be 98 (± 16) s − 1 at 295 K in pH 7 phosphate buffer solution, which is very close to the value reported in the absence of ionic liquid. This suggests that the ionic liquid used here in the HRP–chi–[C 4 mim][BF 4 ]/GC electrode does not enhance the rate of electron transfer. k 0 was found to increase systematically with increasing temperature and followed a linear Arrhenius relation, giving an activation energy of 14.20 kJ mol − 1 . The electrode kinetics and activation energies obtained are identical to those reported for HRP films in aqueous media. This leads us to question if the use of RTIL films provide any unique benefits for enzyme/protein voltammetry. Rather the films may likely contain aqueous zones in which the enzymes are located and undergo electron transfer.