Cu-based Polyoxometalate Catalyst for Efficient Catalytic Hydrogen Evolution

Abstract

Copper-based complexes have been largely neglected as potential water reduction catalysts. This article reports the synthesis and characterization of a tetra-copper-containing polyoxotungstate, Na3K7[Cu4(H2O)2(B-α-PW9O34)2]·30H2O (Na3K7-Cu4P2). Cu4P2 is a water-compatible catalyst for efficient visible-light-driven hydrogen evolution when coupled to (4,4'-di-tert-butyl-2,2'-dipyridyl)-bis(2-phenylpyridine(1H))-iridium(III) hexafluorophosphate ([Ir(ppy)2(dtbbpy)][PF6]) as a light absorber and triethanolamine (TEOA) as sacrificial electron donor. Under minimally optimized conditions, a turnover number (TON) of ∼1270 per Cu4P2 catalyst is obtained after 5 h of irradiation (light-emitting diode; λ = 455 nm; 20 mW); a photochemical quantum efficiency of as high as 15.9% is achieved. Both oxidative and reductive quenching pathways are observed by measuring the luminescence intensity of excited state [Ir(ppy)2(dtbbpy)](+*) in the presence of Cu4P2 or TEOA, respectively. Many stability studies (e.g., UV-vis absorption, FT-IR, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy) show that catalyst Cu4P2 undergoes slow decomposition under turnover conditions; however, both the starting Cu4P2 as well as its molecular decomposition products are the dominant catalytically active species for H2 evolution not Cu or CuOx particles. Considering the high abundance and low cost of copper, the present work provides considerations for the design and synthesis of efficient, molecular, water-compatible Cu-based water reduction catalysts.

Recent Advances in First‐Row Transition Metal Clusters for Photocatalytic Water Splitting

“…In 2016, the Na 3 K 7 [Cu 4 (H 2 O) 2 (B‐α‐PW 9 O 34 ) 2 ] (Na 3 K 7 ‐Cu 4 P 2 ) were reported. It had an optimized TON of ∼1270 per Cu 4 P 2 catalyst after 5 h of irradiation (LED; λ=455 nm; 20 mW) with [Ir(ppy) 2 (dtbbpy)][PF 6 ] as photosensitizer and TEOA as sacrificial electron donor …”

“…[104] This dimeric polyanion consists of two A-α-[SiW 9 6 ] as photosensitizer and TEOA as sacrificial electron donor. [105] Another tellurous copper cluster Na 28 (Figure 10). [106] Because of the template effects of tellurite anions, the structure was stabilized strongly.…”

Multi-Tasking POM Systems

“…However, POMs are quite active as catalysts for multi-electron reduction (reduction of H 2 O to H 2 or CO 2 to carbon-based fuel molecules)(Wang et al, 2016 ; Gumerova and Rompel, 2018 ). Several POMs that are efficient water reduction catalysts under visible-light-driven or dark conditions have been reported (Lv et al, 2014 , 2015 , 2016 ), and some POMs facilitate CO 2 reduction under appropriate conditions (Ettedgui et al, 2010 ; Wang et al, 2016 ). One of the primary applications that has been the subject of extensive research within the field of POMs has been the catalysis of water oxidation.…”

Polyoxometalate‐Decorated g‐C3N4‐Wrapping Snowflake‐Like CdS Nanocrystal for Enhanced Photocatalytic Hydrogen Evolution

“…[34] In parallel, polypyrrole (PPy), with as imple preparation,h igh electrical conductivity,a nd relativelyl ow cost, has usually been integrated with CdS to boost the photocatalytic activity of the composite materialb yi ncreasing its electron conductivity ands tability. [35] In addition to the above, the number of catalytic active sites on the surface of materials can greatly influence the photocatalytic activity.T of urtheri ncreaset he number of active sites, polyoxometalates (POMs) [36][37][38][39] combined with CdS have been studied [40,41] due to their excellent redoxp roperties and structural stability. However,P OMs only have ar esponse to ultravio-let light.…”

“…In addition to the above, the number of catalytic active sites on the surface of materials can greatly influence the photocatalytic activity. To further increase the number of active sites, polyoxometalates (POMs) combined with CdS have been studied due to their excellent redox properties and structural stability. However, POMs only have a response to ultraviolet light.…”