The value of enzymes in solar fuels research – efficient electrocatalysts through evolution

Abstract

Enzymes which evolved more than 2 billion years ago set exceptional standards for electrocatalysts being sought today.

Theoretical Study of O2 Reduction and Water Oxidation in Multicopper Oxidases

“…In the present study, this reduction reaction is therefore presented first, even though the study was initiated by an interest in the reverse oxidation reaction of water. 10 The full reduction cycle was studied, where the electrons were taken from Cu T1 and the protons from water at pH = 7, with a total cost of 387.3 kcal/mol for one (H + , e – ); see above. The energy diagram for the full reduction cycle has not been computationally studied before, and, as shown below, the inclusion of the explicit reduction steps is important for determining the overall rate.…”

“…The main objective of the present study was to investigate both the forward reduction reaction and the reverse oxidation reaction of water, which has recently been studied by electrochemistry. 10 To drive the reaction backward, a much higher redox potential of 1.23 V had to obviously be used compared to 0.46 V for the forward reduction reaction. However, this increase was not enough, and the pH also had to be increased from 7.0 to 10.5, which makes it correspondingly easier to release the protons to water.…”

“…Using an experimental redox potential of 0.46 V for the reductant and an energy of 279.8 kcal/mol for a proton in water leads to a very similar value of 389.1 kcal/mol. The oxidation of water was performed at pH = 10.5 with a redox potential of 1.23 V for the oxidant, 10 which leads to a total driving force of −65.8 kcal/mol. Fitting to that value, a gain of 411.7 kcal/mol for the donation of a (H + , e – ) couple from the Cu 3 cluster is obtained.…”

Serine is the molecular source of the NH(CH2)2 bridgehead moiety of the in vitro assembled [FeFe] hydrogenase H-cluster

“…2 This has led to intense focus on [FeFe] hydrogenases for sustainable production of H 2 and the design of fuel cells. 3 The active site of [FeFe] hydrogenases is a six-iron cofactor called the H-cluster (Scheme 1), which consists of a canonical cuboid [4Fe-4S] H subcluster linked through a bridging cysteine (Cys) residue to a binuclear [2Fe] H subcluster in which the two iron ions are coordinated by three CO, two CN À and an azadithiolate (adt, NH(CH 2 S À ) 2 ) bridging ligand. The [2Fe] H subcluster has been proposed to be the site for H 2 binding and hydride formation, 4,5 which serves as a natural blueprint for designing small molecule catalysts for hydrogen evolution reactions.…”

Mechanism and Application of the Catalytic Reaction of [NiFe] Hydrogenase: Recent Developments

“…Direct biophotolysis of water is the most efficient energy process, since it converts water directly to H 2 and O 2 using sunlight without producing organic intermediates. Conversion of water to H 2 using artificial solar fuels is considered as an effective strategy to help meet future renewable energy requirements . O 2 ‐tolerant [NiFe] H 2 ases (such as Pf and Ec [NiFe] H 2 ases) are promising candidates for biotechnological photohydrogen production, since they can be used under air.…”