Cobalt–Salen Complexes as Catalyst Precursors for Electrocatalytic Water Oxidation at Low Overpotential

Abstract

Water oxidation is an important half-reaction to achieve overall water splitting. In this present study, we show that a series of molecular cobalt-salen complexes can serve as catalyst precursors to form nanostructured and amorphous cobalt-based thin films during electrodeposition, which can catalyze the water oxidation reaction at low overpotentials. Cyclic voltammetry and bulk electrolysis using the cobalt-based film electrodes demonstrated obvious catalytic currents in 0.1 M KBi solution at pH 9.2. The onset catalytic potentials of the catalyst films are at ~0.84 V (vs. Ag/AgCl) with a film made by electrodeposition of cobalt-salen complex 2 on FTO and at ~0.85 V for complex 4. Oxygen gas bubbles were clearly see on the FTO electrode when the applied potential was above the onset potential. The Tafel plots using a catalyst film made of complex 4 showed that appreciable catalytic current was observed starting at η = 0.26 V for the film (a current density of 0.1 mA/cm 2 required η = 290 mV), accompanied by a Faradic efficiency > 93% at 1.2 V.The catalyst film was further characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS).

Earth-abundant metal complexes as catalysts for water oxidation; is it homogeneous or heterogeneous?

“…86 Among the investigated complexes, complex 1 ( Figure 1) exhibited a maximum water oxidation activity of 93% Faradaic efficiency at ~350mV overpotential. Therefore, catalyst films were prepared on FTO electrodes using the complexes thereafter; FTO electrodes were invoked as working electrode for bulk electrolysis measurement in 0.1M KBr solution (pH 9.2) at 1.2V vs Ag/AgCl.…”

Homogeneous and Heterogeneous Photocatalytic Water Oxidation by Persulfate

“…Based on the electrospray ionization mass spectrum (ESI‐MS), 1 H NMR and XPS analyses, the precipitates derived from Co II (salen) during the photocatalytic water oxidation are composed of a mixture of Co III containing oxide and/or Co III hydroxide . Cobalt‐salen complexes were also reported to serve as precursors to deposit nanostructured amorphous catalyst films for catalytic water oxidation with high activity …”

“…[95] Cobalt-salen complexes were also reported to serve as precursors to deposit nanostructured amorphous catalyst films for catalytic water oxidation with high activity. [96] Various iron complexes and Fe(ClO 4 ) 3 also act as precatalysts for the photocatalytic water oxidation by persulfate with [Ru(bpy) 3 ] 2 + at pH 8.5 to produce nanoparticles (Table 2), which were isolated and found to be Fe 2 O 3 using various techniques, including energy-dispersive X-ray spectroscopy and XPS. [97] a-Fe 2 O 3 nanoparticles prepared with ad iameter of 15-70 nm exhibited as imilarc atalytic reactivity with aT ON of 58 compared to Fe(ClO 4 ) 3 used as ap recatalyst, which gave aT ON of 57.…”

Computational characterization of competing energy and electron transfer states in bimetallic donor-acceptor systems for photocatalytic conversion

“…These include catalysts of carbon dioxide reduction: trans(Cl)–Ru(bpy)(CO) 2 Cl 2 or Ru 58 and Re(4,4′-dimethyl-bpy)(CO) 3 Br or Re . 59 Catalysts used for hydrogen production or proton reduction catalysts: a cobalt–salen complex, 6,6′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene)) bis(methanylylidene))bis-(2,4-ditert-butylphenol)cobalt(III) or Co1 60 and [Co III (Cp*)(bpy)(OH)] 2+ where Cp* = η 5 -pentamethylcyclopentadienyl or Co2 . 61 Catalysts used for oxygen production: [Rh III (dmbpy) 2 Cl 2 + ] where dmbpy = 4,4′-dimethyl-2,2′-bipyridine or Rh , 62 (2,5-dpp)PdCl 2 with 2,5-di(pyridine-2-yl)pyrazine or Pd1 , 63 (2,6-dpp)PdCl 2 with 2,6-di(pyridine-2-yl)pyrazine or Pd2 , 64 [Co III (CR)Cl 2 ] + where CR = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo (11.3.1)-heptadeca-1(17),2,11,13,15-pentaene) or Co3 , 65 and 5-[4-(5-carboxyl-2,7-di-tert-butyl-9,9-dimethylxanthene)]-10,15,20-tris(pentafluoro-phenyl)porphyrinatocobalt(I) or Co4 .…”