Copper-based water reduction catalysts for efficient light-driven hydrogen generation

Photoactive Copper Complexes: Properties and Applications

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Performance of enhanced DuBois type water reduction catalysts (WRC) in artificial photosynthesis - effects of various proton relays during catalysis

Inspired by natural photosynthesis, features such as proton relays have been integrated into water reduction catalysts (WRC) for effective production of hydrogen. Research by DuBois et al. showed the crucial influence of these relays, largely in the form of pendant amine functions. In this work catalysts are presented containing innovative diphosphinoamine ligands: [M(ii)Cl2(PNP-C1)], [M(ii)(MeCN)2(PNP-C1)]2+, [M(ii)(PNP-C1)2]2+, and [M(ii)Cl(PNP-C2)]+ (M = Pt2+, Pd2+, Ni2+, Co2+; PNP-C1 = N,N-bis{(di(2-methoxyphenyl)phosphino)methyl}-N-alkylamine, PNP-C2 = N,N-bis{(di(2-methoxyphenyl)phosphino)ethyl}-N-alkylamine and alkyl = Me, Et, iso-Pr, Bz). Synthetic strategies and detailed characterisation are covered, including 1H-, 13C-, and 31P-NMR analysis, mass spectroscopy and single crystal X-ray diffractometry (XRD). The catalytic properties have been explored by changing the pendant amines and auxiliary methoxy coordination sites, as well as enlarging the ligand backbone. Moreover, confirmed by density functional theory (DFT) calculations based on XRD data in vacuo and solvent environment, two very different catalytic cycles are proposed. PNP-C1 shows a classical proton relay, whereas PNP-C2 allows an additional coordination of nitrogen, acting optionally like a pincer. Through new insights into efficiency and stability-increasing influences of proton relays in general, their number per metal centre, an enlarged ligand backbone and the use of solvato instead of halogenido complexes, substantial improvements have been made in catalytic performance over the DuBois et al. catalysts and recently self-made WRCs. The turnover number (TON) related to the single site of cost-efficient nickel WRCs is increased from 11.4 to 637, whereas a corresponding palladium catalyst gives TON as high as 2289.

Mini-review on an engineering approach towards the selection of transition metal complex-based catalysts for photocatalytic H2 production

Advances in transition-metal (Ru, Co, Cu, and Fe) complex-based catalysts since 2000 are briefly summarized in terms of catalyst selection and application for photocatalytic H₂ evolution.

Efficient photocatalytic water reduction by a cobalt(ii) tripodal iminopyridine complex

Enhanced reactivity is observed in a cobalt tripodal iminopyridine WRC bearing a metal active site with a trigonal pyramidal coordination geometry.

A Highly Active and Robust Copper-Based Electrocatalyst toward Hydrogen Evolution Reaction with Low Overpotential in Neutral Solution

Although significant progress has been made recently, copper-based materials have long been considered to be ineffective catalysts toward the hydrogen evolution reaction (HER), in most cases, requiring high overpotentials more than 300 mV. We report here that a Cu(0)-based nanoparticle film electrodeposited in situ from a Cu(II) oxime complex can act as a highly active and robust HER electrocatalyst in neutral phosphate buffer solution. The as-prepared nanoparticle film is of poor crystallization, which incorporates significant amounts of oxime ligand residues and buffer anions PO₄^3-. The proposed mechanism suggests that the Cu(0)-based nanoparticle film is activated with incorporated or adsorbed PO₄^3- anions and the PO₄^3- anions-anchored sites might serve as the actual catalytic active sites with efficient proton transport mediators. Catalysis occurs with a low onset overpotential (η) of 65 mV, and a current density of 1 mA/cm² can be achieved with η = 120 mV. The nanoparticle film shows an excellent catalytic durability with slightly rising current density during electrolysis, presumably due to further incorporation or adsorption of PO₄^3- anions in the process. This electrocatalyst not only forms in situ from earth-abundant materials but also operates in neutral water with low overpotential and high stability.