Spectroscopic Characterisation of a Bio‐Inspired Ni‐Based Proton Reduction Catalyst Bearing a Pentadentate N₂S₃ Ligand with Improved Photocatalytic Activity

Abstract

Inspired by the sulfur‐rich environment found in active hydrogenase enzymes, a Ni‐based proton reduction catalyst with pentadentate N2S3 ligand was synthesised. When coupled with [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N2S2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time‐resolved X‐ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The NiII catalyst undergoes a photoinduced metal‐centred reduction to form a NiI intermediate with distorted square‐bipyramidal geometry. Further kinetic analyses revealed differences in charge‐separation dynamics between the pentadentate and tetradentate forms.

Photocatalytic Hydrogen Evolution by a De Novo Designed Metalloprotein that Undergoes Ni‐Mediated Oligomerization Shift

“…It is known that the H 2 production activity in low acidic pH is controlled by the acidity of the SED [3c,8k,13,18] . The protonated form of ascorbic acid (pK a ∼4.1) is a sluggish electron donor to photoexcited *Ru II compared to its conjugate base [3c,13,19] .…”

Effect of metal centers of complexes bearing bipyridine ligand for electrochemical‐ and photochemical‐driven hydrogen evolution

“…[ 27 ] As can be seen from Figure 2b, the CVs of complex 1 almost remained unchanged in the presence of (AcOH) with the Co II/I process, while the Co I/0 couple changed significantly, indicating that the Co I/0 couple is responsible for proton reduction. [ 28,29 ] Similarly, the Ni I/0 couple of complex 2 is responsible for proton reduction (Figure 2c). As the acid concentration increased, the peak current of this reduction peaks in CVs increased linearly.…”

“…[27] As can be seen from Figure 2b, the CVs of complex 1 almost remained unchanged in the presence of (AcOH) with the Co II/I process, while the Co I/0 couple changed significantly, indicating that the Co I/0 couple is responsible for proton reduction. [28,29] Similarly, the Ni I/0 couple of F I G U R E 2 (a) Cyclic voltammograms (CVs) of 1.7-mM complexes 1 (black) and 2 (red) in dimethylformamide (DMF) solution. CVs of 1.7-mM complex 1 (b) and complex 2 (c) with varying concentrations of acetic acid in DMF, Fc/Fc + internal standard (*) complex 2 is responsible for proton reduction (Figure 2c).…”

Asynchronous x-ray multiprobe data acquisition for x-ray transient absorption spectroscopy

“…X-ray Multiprobe data acquisition 1 (XMP DAQ) is a technique for XTA spectroscopy that measures probe data from every timedelayed x-ray pulse after the laser, in a single acquisition. This allows efficient observation of XTA spectral dynamics over a broad temporal range (∼100 μs), making XMP DAQ an ideal tool for characterizing light induced processes across relatively long time scales [2][3][4][5][6][7] such as diffusion-limited photochemical reactions. Figures 1(a) and 1(b) illustrate the pump-probe synchronization concept employed in previous implementations of XMP DAQ.…”