Proton reduction by molecular catalysts in water under demanding atmospheres

Abstract

The electrocatalytic proton reduction activity of a Ni bis(diphosphine) (NiP) and a cobaloxime (CoP) catalyst has been studied in water in the presence of the gaseous inhibitors O2 and CO. CoP shows an appreciable tolerance towards O2, but its activity suffers severely in the presence of CO. In contrast, NiP is strongly inhibited by O2, but produces H2 under high CO concentrations.

Oxygen-tolerant proton reduction catalysis: much O2 about nothing?

“…78 The study used a water-soluble [Et 3 NH][Co III Cl(dimethylglyoximato) 2 (pyridyl-4-hydrophosphonate)] catalyst ( Figure 6 shows fully protonated complex 1A) and explored changes in activity under varying levels of O 2 . 79 Catalytic currents were seen under N 2 and O 2 (Figure 7a) but not CO, a known catalytic inhibitor ( Figure 7b). 79 Catalytic currents were seen under N 2 and O 2 (Figure 7a) but not CO, a known catalytic inhibitor ( Figure 7b).…”

“…96 Comparison of these complexes to biological structures will be useful in understanding the effects of O 2 inhibition in both classes of catalyst. 79 In its native Ni 2+ oxidation state this catalyst is air stable, suggesting that a reduced form of the catalyst is susceptible to reaction with ROS/O 2 . A recent study of O 2 tolerance with a Ni bis(diphosphine) catalyst (1F, Figure 9) was consequently carried out by our group.…”

“…After repurging the aerobic catalyst solution with N 2 and repeating CPE, the cobaloxime regained 100% of its initial activity, suggesting the drop in activity under air was a result of competitive O 2 reduction by the cobaloxime and not O 2 sensitivity. 79 The photosensitiser will also react with O 2 during catalysis, lowering the rate of electron transfer to the catalyst and producing ROS. Catalysis was driven photochemically using either a heterogeneous Ruphotosensitised TiO 2 nanoparticle system or a homogeneous dye, eosin Y, and the evolved H 2 was measured under increasing concentrations of O 2 .…”

“…88 Proficient reduction of O 2 and ROS to harmless species by these catalysts may explain their limited deactivation in a similar manner to O 2tolerant hydrogenases. 79 The cyclic phosphine ligand-set coordinated to Ni contains pendant amines, which serve as proton relays that has led to TOFs comparable to hydrogenases. 96 Comparison of these complexes to biological structures will be useful in understanding the effects of O 2 inhibition in both classes of catalyst.…”

A Poly(cobaloxime)/Carbon Nanotube Electrode: Freestanding Buckypaper with Polymer‐Enhanced H2‐Evolution Performance

“…[13][14][15][16] Moreover,t hey exhibit high proton-reduction activity at ar elatively low overpotential [17] and can operate in aqueous solutions [18,19] even under aerobic conditions. [20,21] Recently,v ersatile strategies were reported for their immobilization onto metal-oxide [13,22] and carbon-based [23][24][25] surfaces for applications in electro-and photoelectrocatalytic H 2 production. Despite this progress, amajor drawback and limitation in their development is their poor stability,w hich is mainly due to degradation of the equatorial ligand or decoordination of the axial ligand under catalytic conditions.…”