Hai-Hua Huang

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.

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.

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.

A Copper(II) Molecular Catalyst for Efficient and Selective Photochemical Reduction of CO2 to CO in a Water-Containing System

A catalyst developed from a CuII complex of (Et4 N)[Cu(pyN2Me2 )(HCO2 )]⋅0.5 CH3 OH⋅H2 O (1⋅0.5 CH3 OH⋅H2 O; pyN2Me2 =bis(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate(2-)) shows a high activity to catalyze the reduction reaction of CO2 to CO driven by visible light in 4:1 acetonitrile/water (v:v) using [Ru(phen)3 ](PF6 )2 as photosensitizer and TEOA as sacrificial reductant, with a high TON of 9900 and a high CO selectivity of 98 %. The results of isotope labeling experiment, durability tests and energy dispersive spectroscopy reveal that 1 is robust during the photocatalytic process.

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.