The water-gas shift (WGS) reaction (CO + H(2)O <==> CO(2) + H(2)) is of major industrial significance in the production of H(2) from hydrocarbon sources. High temperatures are required, typically in excess of 200 degrees C, using d-metal catalysts on oxide supports. In our study the WGS process is separated into two half-cell electrochemical reactions (H(+) reduction and CO oxidation), catalyzed by enzymes attached to a conducting particle. The H(+) reduction reaction is catalyzed by a hydrogenase, Hyd-2, from Escherichia coli, and CO oxidation is catalyzed by a carbon monoxide dehydrogenase (CODH I) from Carboxydothermus hydrogenoformans. This results in a highly efficient heterogeneous catalyst with a turnover frequency, at 30 degrees C, of at least 2.5 s(-1) per minimum functional unit (a CODH/Hyd-2 pair) which is comparable to conventional high-temperature catalysts.
[Show abstract][Hide abstract] ABSTRACT: The enterobacterium Escherichia coli synthesizes two H2 uptake enzymes, Hyd-1 and Hyd-2. We show using precise electrochemical kinetic measurements that the properties of Hyd-1
and Hyd-2 contrast strikingly, and may be individually optimized to function under distinct environmental conditions. Hyd-2
is well suited for fast and efficient catalysis in more reducing environments, to the extent that in vitro it behaves as a bidirectional hydrogenase. In contrast, Hyd-1 is active for H2 oxidation under more oxidizing conditions and cannot function in reverse. Importantly, Hyd-1 is O2 tolerant and can oxidize H2 in the presence of air, whereas Hyd-2 is ineffective for H2 oxidation under aerobic conditions. The results have direct relevance for physiological roles of Hyd-1 and Hyd-2, which are
expressed in different phases of growth. The properties that we report suggest distinct technological applications of these
[Show abstract][Hide abstract] ABSTRACT: A study of hybrid, enzyme-modified nanoparticles able to produce H(2) using visible light as the energy source has been carried out to establish per-site performance standards for H(2) production catalysts able to operate under ambient conditions. The [NiFeSe]-hydrogenase from Desulfomicrobium baculatum (Db [NiFeSe]-H) is identified as a particularly proficient catalyst. The optimized system consisting of Db [NiFeSe]-H attached to Ru dye-sensitized TiO(2), with triethanolamine as a sacrificial electron donor, produces H(2) at a turnover frequency of approximately 50 (mol H(2)) s(-1) (mol total hydrogenase)(-1) at pH 7 and 25 degrees C, even under the typical solar irradiation of a northern European sky. The system shows high electrocatalytic stability not only under anaerobic conditions but also after prolonged exposure to air, thus making it sufficiently robust for benchtop applications.
Journal of the American Chemical Society 11/2009; 131(51):18457-66. DOI:10.1021/ja907923r · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Photoelectrocatalytic cells for water splitting should combine one or two photosensitive units with a wateroxidationcatalyst at the anode and a hydrogen evolution catalyst at the cathode. In this perspective article, we first show how a chemist can take the naturally occurring multi-electron catalysts for these two electro- and photochemical reactions, photosystem II and hydrogenases, as a source of inspiration for the design of original, efficient and robust molecular catalysts. The focus of this article is given to the immobilisation of these natural or bio-inspired catalysts onto conducting surfaces and the design of electrode and photoelectrode materials for hydrogen evolution/uptake and wateroxidation.
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