Jia-Wei Wang

A Dinuclear Cobalt Cryptate as a Homogeneous Photocatalyst for Highly Selective and Efficient Visible-Light Driven CO2 Reduction to CO in CH3CN/H2O Solution

A dinuclear cobalt complex [Co2 (OH)L1 ](ClO4 )3 (1, L1 =N[(CH2 )2 NHCH2 (m-C6 H4 )CH2 NH(CH2 )2 ]3 N) displays high selectivity and efficiency for the photocatalytic reduction of CO2 to CO in CH3 CN/H2 O (v/v=4:1) under a 450 nm LED light irradiation, with a light intensity of 100 mW cm-2 . The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s-1 , respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two CoII ions within 1, which is strongly supported by the results of control experiments and DFT calculations.

A Nickel(II) Complex as a Homogeneous Electrocatalyst for Water Oxidation at Neutral pH: Dual Role of HPO42− in Catalysis

A new mononuclear nickel complex, featuring two cis‐relative labile sites, is reported as a homogeneous electrocatalyst for water oxidation in a neutral phosphate buffer. The water oxidation catalysis can be initiated at a moderate overpotential of approximately 0.48 V. Mechanistic studies reveal that the oxidation of water by a two‐electron oxidized species of the nickel catalyst is feasible, with formation of a peroxide intermediate through intramolecular O−O coupling. Interestingly, it has been found that the buffer base (HPO42−) plays a dual role in the catalytic system: it acts as a proton acceptor to expedite proton‐coupled electron transfer (PCET) during catalysis, but it also suppresses the electrocatalysis through an anation process.

A Highly Selective and Robust Co(II)-Based Homogeneous Catalyst for Reduction of CO2 to CO in CH3CN/H2O Solution Driven by Visible Light

Visible-light driven reduction of CO2 into chemical fuels has attracted enormous interest in the production of sustainable energy and reversal of the global warming trend. The main challenge in this field is the development of efficient, selective, and economic photocatalysts. Herein, we report a Co(II)-based homogeneous catalyst, [Co(NTB)CH3CN](ClO4)2 (1, NTB = tris(benzimidazolyl-2-methyl)amine), which shows high selectivity and stability for the catalytic reduction of CO2 to CO in a water-containing system driven by visible light, with turnover number (TON) and turnover frequency (TOF) values of 1179 and 0.032 s-1, respectively, and selectivity to CO of 97%. The high catalytic activity of 1 for photochemical CO2-to-CO conversion is supported by the results of electrochemical investigations and DFT calculations.

The synergistic catalysis effect within a dinuclear nickel complex for efficient and selective electrocatalytic reduction of CO2 to CO

Developing cheap and earth-abundant catalysts for an efficient and selective reduction of CO2 is a promising approach to cut down the increasing emissions of CO2 and obtain valuable fuels/chemicals simultaneously. Here, we present a dinuclear nickel complex, [Ni2L1](ClO4)4 (1, L1 = 1,2-bis((5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)methyl)benzene), which shows an excellent performance for the electrocatalytic reduction of CO2 to CO, with a Faradaic efficiency of 95%, and turnover number (TON) and turnover frequency (TOF) values of 4.1 × 106 and 190.0 s−1, respectively. Electrochemical experiments and density functional theory (DFT) calculations revealed that the excellent catalytic performance of 1 is attributed to the synergistic catalysis effect between two Ni centers within 1.

Template-directed synthesis of sulphur doped NiCoFe layered double hydroxide porous nanosheets with enhanced electrocatalytic activity for the oxygen evolution reaction

The development of readily available, highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is extremely significant to facilitate water splitting for the generation of clean hydrogen energy. Layered double hydroxides (LDHs) exhibit promising electrocatalytic performance for the OER. However, their electrical conductivity and active sites should be increased for the preparation of more effective OER electrocatalysts based on LDHs for large-scale applications. Herein, we demonstrate a facile and practical pathway for the hierarchical fabrication of three-dimensional (3D) porous sulphur incorporated NiCoFe LDH nanosheets (S-NiCoFe LDH) on carbon cloth (CC). The as-obtained hierarchically structured S-NiCoFe LDH electrode shows superb electrocatalytic activity and stability for the OER, requiring overpotentials as low as 206 mV and 258 mV to achieve current densities of 10 mA cm−2 and 100 mA cm−2 in 1.0 M KOH solution, respectively, making S-NiCoFe LDH one of the most efficient low-cost electrocatalysts for the OER. The enhanced electrocatalytic performance is attributed to the unique 3D hierarchical nanostructure and sulphur doping, which endow the self-supported S-NiCoFe LDH electrode with abundant active sites and superb electrical conductivity. The strategy expands the possibilities for boosting the catalytic activity of LDH-based OER electrocatalysts.

Further insight into the electrocatalytic water oxidation by macrocyclic nickel(II) complexes: the influence of steric effect on catalytic activity

The development of efficient, robust and economical water oxidation catalysts (WOCs) remains a key challenge for water splitting. Herein, three macrocyclic nickel(II) complexes with four, six and eight methyl groups in the ligands have been utilized as homogeneous electrocatalysts for water oxidation in aqueous phosphate buffer at pH 7.0, in which the catalyst with eight methyl groups exhibits the highest catalytic activity, with a large current density of 1.0 mA cm−2 at 1.55 V vs. NHE (750 mV overpotential) in long-term electrolysis. The results of electrochemistry, UV-vis spectroelectrochemistry and DFT calculations suggest that the axially oriented methyl groups in the macrocyclic ligands with eight and six methyl groups can impose a steric effect on the axial position of the NiIII center, which not only results in higher NiIII/II oxidation potentials but also suppresses the axial coordination of phosphate anions with the NiIII center to achieve better catalytic performance. Such a steric effect in homogeneous WOCs has not been reported so far.

Self-Template Synthesis of Co–Se–S–O Hierarchical Nanotubes as Efficient Electrocatalysts for Oxygen Evolution under Alkaline and Neutral Conditions

We develop a facile self-template synthetic method to construct hierarchical Co-Se-S-O (CoSe xS2- x@Co(OH)2) nanotubes on a carbon cloth as a self-standing electrode for electrocatalytic oxygen evolution reaction (OER). In the synthetic process, separate selenization and sulfurization on the Co(OH)F precursor in different solvents have played an important role in constructing CoSe xS2- x (Co-Se-S) hierarchical nanotubes, which was further transformed into the nanotube-like Co-Se-S-O via an in situ electrochemical oxidation process. The Co-Se-S-O obtained by the Kirkendall effect through two stepwise anion-exchange reactions represents the first quaternary Co-Se-S-O nanotube array, which dramatically enhances its surface area and conductivity. Further, it only requires low overpotentials of 230 and 480 mV to achieve a 10 mA cm-2 current density. The OER performance of Co-Se-S-O is much more efficient than that of its monochalcogenide counterparts, as well as the commercial benchmark catalyst IrO2.

Highly efficient oxygen evolution electrocatalysts prepared by using reduction-engraved ferrites on graphene oxide

Rational design and synthesis of efficient, stable and low-cost electrocatalysts for oxygen evolution reaction (OER) is critical for renewable energy conversion and storage. Herein, the reduction-engraved strategy was adopted to treat crystalline ferrite nanoparticles, which are highly dispersed on graphene oxide (GO) nanosheets. This reduction treatment generated abundant oxygen vacancies on the surface of nano-scale ferrites and dramatically enhanced their surface area, ensuring that the ferrite nanoparticles possess more accessible active sites for OER, and improve their electronic conductivity. Reduced cobalt/nickel ferrite (Co0.5Ni0.5Fe2O4, r-CNF), cobalt ferrite (CoFe2O4, r-CF) and nickel ferrite (NiFe2O4, r-NF) nanoparticles anchoring on the ultrathin GO nanosheets can act as highly active, stable and low-cost OER electrocatalysts in 1.0 M KOH solution. The r-CNF (Co : Ni = 1 : 1) on GO (r-CNFg) shows the best OER performance among the ferrite-based OER electrocatalysts, with an overpotential of 210 mV at 10 mA cm−2 in 1.0 M KOH solution, much more efficient than that of a commercial benchmark catalyst IrO2 (230 mV). The catalytic current density of r-CNFg at 1.49 V vs. RHE is about 50 times higher than that of CNF and CNFg. Also, it exhibits prominent electrochemical stability over 500 h in 1.0 M KOH.

Highly Efficient and Selective Visible-Light Driven CO2-to-CO Conversion by a Co(II) Homogeneous Catalyst in H2O/CH3CN Solution

The photochemical reduction of CO2 to chemical resources has displayed the promise to solve energy and environmental problems. To facilitate this reaction, a considerable challenge is to design not only highly efficient and selective, but also economic catalysts. In this study, we report a homogeneous catalyst, [CoL1(CH3CN)](ClO4)2 (1, L1=Tris[2‐(iso‐propylamino)ethyl]amine) which displays high activity and selectivity for CO2 reduction to CO driven by visible light in a water‐containing system, with turnover numbers (TONCO) and turnover frequencies (TOF), and CO selectivity values of 44800, 1.24 s−1 and 97 %, respectively. The excellent performances of 1 for the photocatalytic CO2‐to‐CO conversion is confirmed by control experiments and its catalytic mechanism is corroborated by DFT calculations.

Fe-CoP Electrocatalyst Derived from a Bimetallic Prussian Blue Analogue for Large-Current-Density Oxygen Evolution and Overall Water Splitting

Abstract Industrial application of overall water splitting requires developing readily available, highly efficient, and stable oxygen evolution electrocatalysts that can efficiently drive large current density. This study reports a facile and practical method to fabricate a non‐noble metal catalyst by directly growing a Co‐Fe Prussian blue analogue on a 3D porous conductive substrate, which is further phosphorized into a bifunctional Fe‐doped CoP (Fe‐CoP) electrocatalyst. The Fe‐CoP/NF (nickel foam) catalyst shows efficient electrocatalytic activity for oxygen evolution reaction, requiring low overpotentials of 190, 295, and 428 mV to achieve 10, 500, and 1000 mA cm−2 current densities in 1.0 m KOH solution. In addition, the Fe‐CoP/NF can also function as a highly active electrocatalyst for hydrogen evolution reaction with a low overpotential of 78 mV at 10 mA cm−2 current density in alkaline solution. Thus, the Fe‐CoP/NF electrode with meso/macropores can act as both an anode and a cathode to fabricate an electrolyzer for overall water splitting, only requiring a cell voltage of 1.49 V to afford a 10 mA cm−2 current density with remarkable stability. This performance appears to be among the best reported values and is much better than that of the IrO2‐Pt/C‐based electrolyzer.