Mechanistic Details for Cobalt Catalyzed Photochemical Hydrogen Production in Aqueous Solution: Efficiencies of the Photochemical and Non-Photochemical Steps

Abstract

A detailed examination of each step of the reaction sequence in the photochemical sacrificial hydrogen generation system consisting of [Ru(bpy)3](2+)/ascorbate/[Co(DPA-bpy)OH2](3+) was conducted. By clearly defining quenching, charge separation, and back electron transfer in the [Ru(bpy)3](2+)/ascorbate system, the details necessary for evaluation of the efficiency of water reduction with various catalysts are provided. In the particular Co(III) catalyst investigated, it is clear that the light induced catalytic process is considerably less efficient than the electrocatalytic process. A potential source of catalyst inefficiency in this system is reduction of the products formed in oxidation of the sacrificial electron donor. The data provided for excited state quenching and charge separation in this particular aqueous system are meant to be used by others for thorough investigation of the quantum efficiencies of other aqueous homogeneous and nanoheterogeneous catalysts for water reduction.

An Efficient RuII–RhIII–RuII Polypyridyl Photocatalyst for Visible‐Light‐Driven Hydrogen Production in Aqueous Solution

“…Since the Ru* lifetime in Ru 2 Rh in the absence of HA À is only moderately decreased (22.5 %) as compared to that in the regular Ru complex (see Figure S7), we infer that the oxidative quenching of Ru* is not efficient in the trinuclear photocatalyst, and consequently, that the initial photoinduced electron-transfer process mainly occurs by reductive quenching with HA À . [17] Furthermore, owing to the very fast reduction of Rh III by Ru I in Ru 2 Rh by a subnanosecond electron shift, no strong transient absorption typical of the Ru I species was detected at 510 nm [44] in the 100-500 ns time range (Figure 2 a), in contrast to observations with the bimolecular photocatalytic system (Figure 2 b). For these complexes, the oxidative quenching of the Ru excited state by the Rh unit, with rates ranging from 1.1 10 6 to 3 10 9 s À1 , is faster than in Ru 2 Rh (4.9 10 5 s À1 ; see the Supporting Information).…”

Ru–protein–Co biohybrids designed for solar hydrogen production: understanding electron transfer pathways related to photocatalytic function

“…In the Ru–ApoFld–CoBF 2 biohybrid, electron transfer occurs via a direct pathway between Ru PS and CoBF 2 . We propose that the signal at 510 nm with ∼22 mOD intensity occurs due to Ru( i ), generated by reductive quenching of the excited state Ru( ii )* with ascorbate (eqn (1)) 47 Ru( ii )*–Co( ii ) + Asc ⇆ Ru( i )–Co( ii ) + Asc + …”

Electrochemical Detection of Transient Cobalt Hydride Intermediates of Electrocatalytic Hydrogen Production

“…[1][2][3][4][5][6] Many cobalt catalysts display desirable catalytic properties, including low overpotential, [7][8][9][10][11] solubility in water, 10,[12][13][14][15][16][17][18][19][20][21][22] and stability towards O2. [23][24][25][26] Several groups have constructed hybrid systems for production of H2 in which a molecular cobalt catalyst has been attached to an electrode surface, [27][28][29][30][31] covalently linked to a photosensitizer, [32][33][34][35][36] or inserted into Photosystem I.…”