Electrocatalytic proton reduction to form dihydrogen (H 2 ) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main-group-element-based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (À 4.6 mA cm À 2 at À 1.7 V vs. Fc/Fc + ) and high selectivity (H 2 Faradaic efficiency of 94 % at À 1.7 V vs. Fc/Fc + ) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOF max ) for H 2 production was obtained as 1099 s À 1 . Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron-chemical-electron-chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction.

The electrochemical reduction of carbon dioxide (CO2) to produce value-added chemicals is of great significance in mitigating environmental and energy concerns. In this work, an iron porphyrin catalyst, FePEG8T, with multiple triazole units tethered to a porphyrin ligand via flexible oxymethylene linkers, is reported for efficient electrocatalytic reduction of CO2 to afford carbon monoxide (CO). The electrocatalyst exhibits an excellent catalytic activity with a current density of −17.5 mA/cm2 and CO Faradaic efficiency of 95% at −2.5 V vs Fc/Fc+ in acetonitrile using water as the proton source. The maximum turnover frequency (TOFmax) was calculated to be 5.5 × 104 s–1 using foot-of-the-wave analysis, which is thirty times higher than the result from our previous zinc complex with the same triazole–porphyrin ligand. Control experiments on an iron porphyrin complex without triazole units confirm the contribution of triazole units on high catalytic activity. Long-term electrolysis of 40 h was also performed and demonstrated high catalyst stability. A normal KIE of 6.92 was obtained with H2O/D2O as the proton source at varying concentration ranges (0.5–5 M), suggesting that protonation of the catalyst–substrate intermediate is a rate-limiting step. Furthermore, the Tafel plot was generated for the catalyst FePEG8T for comparison with previously reported iron porphyrin catalysts. This work demonstrates an efficient CO2 reduction catalyst containing an iron metal center and a flexible triazole in the second coordination sphere toward CO formation with high stability, activity, and selectivity.

Electrochemical carbon dioxide (CO2) reduction is a sustainable approach for transforming atmospheric CO2 into chemical feedstocks and fuels. To overcome the kinetic barriers of electrocatalytic CO2 reduction, catalysts with high selectivity, activity, and stability are needed. Here, we report an iron porphyrin complex, FePEGP, with a poly­(ethylene glycol) unit in the second coordination sphere, as a highly selective and active electrocatalyst for the electrochemical reduction of CO2 to carbon monoxide (CO). Controlled-potential electrolysis using FePEGP showed a Faradaic efficiency of 98% and a current density of −7.8 mA/cm2 at −2.2 V versus Fc/Fc+ in acetonitrile using water as the proton source. The maximum turnover frequency was calculated to be 1.4 × 105 s–1 using foot-of-the-wave analysis. Distinct from most other catalysts, the kinetic isotope effect (KIE) study revealed that the protonation step of the Fe–CO2 adduct is not involved in the rate-limiting step. This model shows that the PEG unit as the secondary coordination sphere enhances the catalytic kinetics and thus is an effective design for electrocatalytic CO2 reduction.

Electrocatalytic hydrogen gas production is considered a potential pathway towards carbon-neutral energy sources. However, the development of this technology is hindered by the lack of efficient, cost-effective, and environmentally benign catalysts. In this study, a main-groupelement-based electrocatalyst, SbSalen, is reported to catalyze the hydrogen evolution reaction (HER) in an aqueous medium. The heterogenized molecular system achieved a Faradaic efficiency of 100 % at À 1.4 V vs. NHE with a maximum current density of À 30.7 mA/cm 2 . X-ray photoelectron spectroscopy of the catalyst-bound working electrode before and after electrolysis confirmed the molecular stability during catalysis. The turnover frequency was calculated as 43.4 s À 1 using redox-peak integration. The kinetic and mechanistic aspects of the electrocatalytic reaction were further examined by computational methods. This study provides mechanistic insights into main-group-element electrocatalysts for heterogeneous small-molecule conversion.

In this work, the electrocatalytic reduction of dichloromethane (CH2Cl2) into hydrocarbons involving a main group element‐based molecular triazole‐porphyrin electrocatalyst H2PorT8 is reported. This catalyst converted CH2Cl2 in acetonitrile to various hydrocarbons (methane, ethane, and ethylene) with a Faradaic efficiency of 70 % and current density of −13 mA cm−2 at a potential of −2.2 V vs. Fc/Fc+ using water as a proton source. The findings of this study and its mechanistic interpretations demonstrated that H2PorT8 was an efficient and stable catalyst for the hydrodechlorination of CH2Cl2 and that main group catalysts could be potentially used for exploring new catalytic reaction mechanisms.

Two-electron-active tetracyanoethylene (TCNE) is studied as an anolyte for nonaqueous redox flow batteries. The TCNE/phenothiazine battery presents a maximum specific capacity density of 23.3 A h L−1 and volumetric energy density of 26 W h L−1.

Potassium-ion batteries (PIBs) are promising energy storage devices owing to the abundance and low cost of potassium. However, the development of PIBs is still in its infancy owing to the poor kinetic diffusivity, limited capacity, and severe side reactions. It is imperative to explore new materials to address the issues of capacity, stability, and cycle life in PIBs. Here, we present a hybrid slurry/flow battery utilizing redox-active organic materials for K+ storage, wherein the indigo slurry serves as the anolyte and K4Fe­(CN)6 solution serves as the catholyte. This battery presented a cycle life of 1000 cycles with a capacity of 18.4 Ah/L and capacity retention of ∼83%. Voltammetry measurements and density functional theory calculations indicated that the redox activity of indigo involves a one-step, double-electron process, instead of a two-step, single-electron process. This work provides new insights into the application of organic compounds as association materials for PIBs.

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