Reversible interconversion of carbon dioxide and formate by an electroactive enzyme

Abstract

Carbon dioxide (CO2) is a kinetically and thermodynamically stable molecule. It is easily formed by the oxidation of organic molecules, during combustion or respiration, but is difficult to reduce. The production of reduced carbon compounds from CO 2 is an attractive proposition, because carbon-neutral energy sources could be used to generate fuel resources and sequester CO 2 from the atmosphere. However, available methods for the electrochemical reduction of CO2 require excessive overpotentials (are energetically wasteful) and produce mixtures of products. Here, we show that a tungsten-containing formate dehydrogenase enzyme (FDH1) adsorbed to an electrode surface catalyzes the efficient electrochemical reduction of CO 2 to formate. Electrocatalysis by FDH1 is thermodynamically reversible-only small overpotentials are required, and the point of zero net catalytic current defines the reduction potential. It occurs under thoroughly mild conditions, and formate is the only product. Both as a homogeneous catalyst and on the electrode, FDH1 catalyzes CO 2 reduction with a rate more than two orders of magnitude faster than that of any known catalyst for the same reaction. Formate oxidation is more than five times faster than CO 2 reduction. Thermodynamically, formate and hydrogen are oxidized at similar potentials, so formate is a viable energy source in its own right as well as an industrially important feedstock and a stable intermediate in the conversion of CO2 to methanol and methane. FDH1 demonstrates the feasibility of interconverting CO2 and formate electrochemically, and it is a template for the development of robust synthetic catalysts suitable for practical applications.electrocatalysis ͉ formate dehydrogenase ͉ formate oxidation ͉ protein film voltammetry ͉ carbon dioxide reduction C arbon dioxide (CO 2 ) is a kinetically and thermodynamically stable molecule that is difficult to chemically activate. As the unreactive product of the combustion of carbon-containing molecules, such as fossil fuels, and biological respiration, it is accumulating in the atmosphere and is a major cause of concern in climate-change scenarios (1, 2). Consequently, catalysts that are able to sequester CO 2 from the atmosphere rapidly and efficiently, to generate reduced carbon compounds for use as fuels or chemical feedstocks, have long been sought after. Organometallic complexes that insert CO 2 into an M-H bond and the use of supercritical CO 2 to facilitate its hydrogenation are two promising approaches to the development of a homogeneous catalytic process (3-5). Extensive efforts to develop electrode materials for the direct, electrochemical reduction of CO 2 have been made also, but so far, they require the application of extreme potentials (are inefficient energetically) or they are nonspecific and produce mixtures of products (4, 6, 7). An efficient and specific method for reducing CO 2 electrochemically has obvious applications in a future energy economy based on the cyclic reduction and oxidation of simple carbon compound...

Strategies for stable anaerobic digestion of vegetable waste

“…This finding supports the importance of tungsten in maintaining the anaerobic process. The requirement for tungsten of methanogens growing on H 2 and CO 2 has long been known [31], and this element has also been reported to play a significant role in propionate degradation [32,33]. Despite this, however, tungsten is not included in most of the commonly-used trace element recipes found in the literature.…”

Direct enzymatic bioelectrocatalysis: differentiating between myth and reality

“…Most commonly, CO 2 reduction has been explored with the aim of producing formate or alkanes/alcohols, although NAD þ reduction to NADH is frequently attempted where NAD-dependent enzymes can support reductive reactions [22][23][24]; Vincent and co-workers [25] have also demonstrated that the coimmobilization of hydrogenase and NAD þ -reducing proteins onto conductive particles can facilitate H 2 -driven NADH production. Recent research has also explored the possibility of reducing dinitrogen (N 2 ) to an important chemical commodity, ammonia (NH 3 ), while simultaneously producing electrical energy [26].…”

Sulphur shuttling across a chaperone during molybdenum cofactor maturation

“…Only few FDHs have been characterized as formate-producing enzymes, most of those identified so far being formate consumers 3 . However, both types of enzymes share high sequence similarity and their reaction can be efficiently reversed by electrocatalysis 4 . FDHs are mononuclear molybdenum (Mo)-or tungsten (W)-containing enzymes belonging to the dimethyl sulphoxide reductase family, an ancient and widespread family in prokaryotes 5,6 .…”