David W. Wakerley

Reversible Interconversion of CO2 and Formate by a Molybdenum-Containing Formate Dehydrogenase

CO2 and formate are rapidly, selectively, and efficiently interconverted by tungsten-containing formate dehydrogenases that surpass current synthetic catalysts. However, their mechanism of catalysis is unknown, and no tractable system is available for study. Here, we describe the catalytic properties of the molybdenum-containing formate dehydrogenase H from the model organism Escherichia coli (EcFDH-H). We use protein film voltammetry to demonstrate that EcFDH-H is a highly active, reversible electrocatalyst. In each voltammogram a single point of zero net current denotes the CO2 reduction potential that varies with pH according to the Nernst equation. By quantifying formate production we show that electrocatalytic CO2 reduction is specific. Our results reveal the capabilities of a Mo-containing catalyst for reversible CO2 reduction and establish EcFDH-H as an attractive model system for mechanistic investigations and a template for the development of synthetic catalysts.

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

Proton reduction catalysts are an integral component of artificial photosynthetic systems for the production of H2. This perspective covers such catalysts with respect to their tolerance towards the potential catalyst inhibitor O2. O2 is abundant in our atmosphere and generated as a by-product during the water splitting process, therefore maintaining proton reduction activity in the presence of O2 is important for the widespread production of H2. This perspective article summarises viable strategies for avoiding the adverse effects of aerobic environments to encourage their adoption and improvement in future research. H2-evolving enzymatic systems, molecular synthetic catalysts and catalytic surfaces are discussed with respect to their interaction with O2 and analytical techniques through which O2-tolerant catalysts can be studied are described.

Photocatalytic Formic Acid Conversion on CdS Nanocrystals with Controllable Selectivity for H2 or CO

Formic acid is considered a promising energy carrier and hydrogen storage material for a carbon-neutral economy. We present an inexpensive system for the selective room-temperature photocatalytic conversion of formic acid into either hydrogen or carbon monoxide. Under visible-light irradiation (λ>420 nm, 1 sun), suspensions of ligand-capped cadmium sulfide nanocrystals in formic acid/sodium formate release up to 116±14 mmol H2 gcat−1 h−1 with >99 % selectivity when combined with a cobalt co-catalyst; the quantum yield at λ=460 nm was 21.2±2.7 %. In the absence of capping ligands, suspensions of the same photocatalyst in aqueous sodium formate generate up to 102±13 mmol CO gcat−1 h−1 with >95 % selectivity and 19.7±2.7 % quantum yield. H2 and CO production was sustained for more than one week with turnover numbers greater than 6×105 and 3×106, respectively.

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

Abstract A freestanding H2‐evolution electrode consisting of a copolymer‐embedded cobaloxime integrated into a multiwall carbon nanotube matrix by π–π interactions is reported. This electrode is straightforward to assemble and displays high activity towards hydrogen evolution in near‐neutral pH solution under inert and aerobic conditions, with a cobalt‐based turnover number (TONCo) of up to 420. An analogous electrode with a monomeric cobaloxime showed less activity with a TONCo of only 80. These results suggest that, in addition to the high surface area of the porous network of the buckypaper, the polymeric scaffold provides a stabilizing environment to the catalyst, leading to further enhancement in catalytic performance. We have therefore established that the use of a multifunctional copolymeric architecture is a viable strategy to enhance the performance of molecular electrocatalysts.

Correction to “Reversible Interconversion of CO2 and Formate by a Molybdenum-Containing Formate Dehydrogenase”

Published: March 24, 2015 Figure 2. Cyclic voltammograms showing reversible CO2 reduction and formate oxidation by EcFDH-H adsorbed on a graphite-epoxy electrode, pH 6.0 (left), 6.8 (middle), and 8.0 (right). The points of intersection (marked with crosses) define the reduction potentials for the CO2/formate interconversion (vertical lines). First voltammetric cycles are shown in black and subsequent cycles (2−4, 10, and 20) in gray. Voltammograms recorded in the absence of substrates are shown as dashed traces. Conditions: 10 mM CO2, 25 10 mM formate, 25 mM of each of four pH buffers (acetate, MES, HEPES, and TAPS), voltammetric scan rate 25 mV s−1, electrode rotation rate 2000 rpm, 23 °C. Addition/Correction

Aerobic Conditions Enhance the Photocatalytic Stability of CdS/CdO x Quantum Dots

Abstract Photocatalytic H2 production through water splitting represents an attractive route to generate a renewable fuel. These systems are typically limited to anaerobic conditions due to the inhibiting effects of O2. Here, we report that sacrificial H2 evolution with CdS quantum dots does not necessarily suffer from O2 inhibition and can even be stabilised under aerobic conditions. The introduction of O2 prevents a key inactivation pathway of CdS (over‐accumulation of metallic Cd and particle agglomeration) and thereby affords particles with higher stability. These findings represent a possibility to exploit the O2 reduction reaction to inhibit deactivation, rather than catalysis, offering a strategy to stabilise photocatalysts that suffer from similar degradation reactions.

Research data supporting "Solar-driven reforming of lignocellulose to H2 with a CdS/CdOx photocatalyst"

Raw data supporting Nature Energy publication: Solar-driven reforming of lignocellulose to H2 with a CdS/CdOx photocatalyst

Plastic waste as a feedstock for solar-driven H2 generation

Solar-driven reforming of plastics offers a simple and low-energy means to turn waste into H2. Here, we report the efficient photoreforming of three commonly produced polymers – polylactic acid, polyethylene terephthalate (PET) and polyurethane – using inexpensive CdS/CdOx quantum dots in alkaline aqueous solution. This process operates under ambient temperature and pressure, generates pure H2 and converts the waste polymer into organic products such as formate, acetate and pyruvate. We further validate the real-world applicability of the system by converting a PET water bottle into H2. This is the first demonstration of visible light-driven, noble metal-free photoreforming of plastic.