A Highly Stable Rhenium−Cobalt System for Photocatalytic H₂ Production: Unraveling the Performance-Limiting Steps

Abstract

Increased long-term performance was found for photocatalytic H(2) production in a homogeneous combination of [Re(NCS)(CO)(3)bipy] (1; bipy = 2,2'-bipyridine), [Co(dmgH)(2)] (dmgH(2) = dimethylglyoxime), triethanolamine (TEOA), and [HTEOA][BF(4)] in N,N-dimethylformamide, achieving TON(Re) up to 6000 (H/Re). The system proceeded by reductive quenching of *1 by TEOA, followed by fast (k(1) = 1.3 x 10(8) M(-1) s(-1)) electron transfer to [Co(II)(dmgH)(2)] and subsequent protonation (K(2)) and elimination (k(3), second-order process in cobalt) of H(2). Observed quantum yields were up to approximately 90% (H produced per absorbed photon). The type of acid had a substantial effect on the long-term stability. A decomposition pathway involving cobalt is limiting the long-term performance. Time-resolved infrared (IR) spectroscopy confirmed that photooxidized TEOA generates a second reducing equivalent, which can be transferred to 1 (70%, k(2e)(-) = 3.3 x 10(8) M(-1) s(-1)) if no [Co(II)(dmgH)(2)] is present.

Photocatalysis: Basic Principles, Diverse Forms of Implementations and Emerging Scientific Opportunities

“…[76b,78] In the tests, precipitation is indeed frequently observed due to the decomposition of the photocatalysts. [79] Finding homogeneous photocatalysts that are stable and can absorb broadly in the solar spectrum is of great importance. [80] In recent years, many efforts have been devoted to heterogenizing homogeneous photocatalysts onto solid substrate (e.g., TiO 2 , SiO 2 , and g-C 3 N 4 ) by adsorption, grafting, and/or electrostatic interaction to achieve better performance.…”

Closing the pressure gap in x-ray photoelectron spectroscopy by membrane hydrogenation

“…1 In these processes, the central metallic element in the WRC is expected to reversibly change its oxidation state through successive electron transfers with a photosensitiser and water, 36 with the subsequent formation of intermediate forms of the WRC. Cobalt dioxime complexes are seen as promising catalysts in this respect, both regarding photo- 36 and electrocatalytic 37 H 2 production. We will focus here on such a compound with the formula C 18 H 23 CoN 6 O 4 (see Fig.…”

Cobalt-dithiolene complexes for the photocatalytic and electrocatalytic reduction of protons in aqueous solutions

“…One of these electrocatalysts, CoðdmgHÞ 2 ðpyrÞCl (dmgH ¼ dimethylglyoximate monoanion) has also been found to be active as a hydrogen generating catalyst when combined with a suitable photosensitizer and sacrificial electron donor (6,10,20). In recently reported photochemical H 2 generation, systems containing cobaloxime catalysts have shown considerable activity (21)(22)(23)(24)(25) with turnover numbers (TONs) as high as 9,000 with respect to chromophore (25)(26)(27). However, one limitation is that the TONs are modest based on catalyst (<300, with TOF <100∕h), and hydrogen production ceases after 6 h of irradiation.…”