Arginine‐Containing Ligands Enhance H₂ Oxidation Catalyst Performance

Abstract

Hydrogenase enzymes use Ni and Fe to oxidize H2 at high turnover frequencies (TOF) (up to 10 000 s−1) and low overpotentials (<100 mV). In comparison, the fastest reported synthetic electrocatalyst, [NiII(PCy2NtBu2)2]2+, oxidizes H2 at 60 s−1 in MeCN under 1 atm H2 with an unoptimized overpotential of ca. 500 mV using triethylamine as a base.1 Here we show that a structured outer coordination sphere in a Ni electrocatalyst enhances H2 oxidation activity: [NiII(PCy2NArg2)2]8+ (Arg=arginine) has a TOF of 210 s−1 in water with high energy efficiency (180 mV overpotential) under 1 atm H2, and 144 000 s−1 (460 mV overpotential) under 133 atm H2. The complex is active from pH 0–14 and is faster at low pH, the most relevant condition for fuel cells. The arginine substituents increase TOF and may engage in an intramolecular guanidinium interaction that assists in H2 activation, while the COOH groups facilitate rapid proton movement. These results emphasize the critical role of features beyond the active site in achieving fast, efficient catalysis.

Photo‐Driven Hydrogen Evolution by an Artificial Hydrogenase Utilizing the Biotin‐Streptavidin Technology

“…Substitution of the serine residue S112 by either an Asp (Sav S112D, TON = 920 after 6 h, light green trace, Figure ,b ) or a Arg (Sav S112R, TON = 970 after 6 h, turquoise trace, Figure ,b ) lead to an increase in TON compared to Sav WT (green trace, Figure ,b ). We speculate that this might be due to the presence of close lying amino acids capable of acting as a proton relay, potentially facilitating outer‐sphere protonation of the Co‐H species, as suggested in related studies . Thus an increase in the rate of H 2 formation at the ArM, and a concomitant removal of reducing equivalents from the system, would be expected.…”

How do H2 oxidation molecular catalysts assemble onto carbon nanotube electrodes? A crosstalk between electrochemical and multi-physical characterization techniques

“…20 were purchased from Paxitech (Grenoble, France). [Ni(P Cy 2 N Arg 2 ) 2 ](BF 4 ) 2 (NiArg) 31 was synthesized according to published procedures. MilliQ water was systematically used.…”

“…25,26 So far the most HOR-active catalyst in this series after immobilization is an arginine derivative [Ni(P 2 Cy N 2 Arg ) 2 ] 7+ (NiArg, Figure 1) designed by Shaw and coworkers. 31 Multiwalled carbon nanotubes (MWNT) form a well-adapted platform for electrode development as they provide both a large surface area to support the catalyst adsorption, 17,18,20,[32][33][34] and a high conductivity in film. 35 Such molecularly-engineered nanomaterials proved operational once implemented in the platinum-group-metal-free (PGM-free) anode of a H 2 /O 2 fuel cell device.…”

Reversible H2 oxidation and evolution by hydrogenase embedded in a redox polymer film

“…Their global implementation in sustainable energy schemes also requires that these catalysts are scalable and robust. 15 Some bioinspired and biological catalysts are made of earth-abundant elements and could thus fulfill the scalability requirement, [16][17][18] but their robustness is often insufficient for direct implementation in energy converting devices, especially because of their sensitivity to oxidative stress and molecular oxygen. [19][20][21][22][23] A recently proposed solution to that problem, based on the incorporation of fragile catalysts into redox-active films serving as a protection matrix against oxidative deactivation, [24][25][26][27][28][29][30][31] enabled us to use the highly O 2 -sensitive [FeFe] hydrogenase 32,33 even under operating fuel cell conditions.…”