The activity of molecular electrocatalysts depends on the interplay of electrolyte composition near the electrode surface, the composition and morphology of the electrode surface, and the electric ...field at the electrode–electrolyte interface. This interplay is challenging to study and often overlooked when assessing molecular catalyst activity. Here, we use surface specific vibrational sum frequency generation (VSFG) spectroscopy to study the solvent and potential dependent activation of Mo(bpy)(CO)4, a CO2 reduction catalyst, at a polycrystalline Au electrode. We find that the parent complex undergoes potential dependent reorientation at the electrode surface when a small amount of N-methyl-2-pyrrolidone (NMP) is present. This preactivates the complex, resulting in greater yields at less negative potentials, of the active electrocatalyst for CO2 reduction.
Abstract
Electrolyzers for CO
2
reduction containing bipolar membranes (BPM) are promising due to low loss of CO
2
as carbonates and low product crossover, but improvements in product selectivity, ...stability, and cell voltage are required. In particular, direct contact with the acidic cation exchange layer leads to high levels of H
2
evolution with many common cathode catalysts. Here, Co phthalocyanine (CoPc) is reported as a suitable catalyst for a zero‐gap BPM device, reaching 53% Faradaic efficiency to CO at 100 mA cm
−2
using only pure water and CO
2
as the input feeds. It is also shown that the cell voltage can be lowered by constructing a customized BPM using TiO
2
water dissociation catalyst, however this is at the cost of decreased selectivity. Switching the pure‐water anolyte to KOH improved both the cell voltage and CO selectivity (62% at 200 mA cm
−2
), but cation crossover could cause complications. The results demonstrate viable strategies for improving a BPM CO
2
electrolyzer toward practical‐scale CO
2
‐to‐chemicals conversion.
In living cells, the overall rates of catalytic reaction chains (cascades) are massively enhanced by nanoconfinement of enzymes in tiny enclosed volumes: presented in such a way, interdependent ...catalysts are highly concentrated, and distances (active site‐to‐active site) across which intermediates and cofactors must diffuse, may be tiny. In a parallel technology exploiting this principle, enzyme cascades are powered, amplified, and monitored in real time as they work in concert, being nanoconfined within the pores of an electrically conductive metal oxide electrode. The technology, nicknamed the electrochemical leaf, mimics chloroplast biosynthesis by exploiting nicotinamide adenine dinucleotide (NADP(H)) recycling catalysed by the flavoenzyme, ferredoxin NADP+ reductase (FNR). Adsorbed on the inner walls of the nanopores, FNR rapidly transfers electrons between the electrode and NADP(H). This activity is coupled to an oxidoreductase enzyme, also nanoconfined within the pores, which recycles the cofactor and selectively synthesises a desired product or senses an analyte. Use of catalyst and cofactor is very efficient. The technology is simple, inexpensive and adaptable, and scalable to both microscopic levels (diagnostics) and macroscopic levels (organic synthesis). Whereas native FNR is specific for NADP(H), the technology can be extended by genetic engineering to include NAD(H) as recycling cofactor.
The electrochemical leaf: represented here as a sheet of titanium foil coated each side with a micron‐scale conductive layer of indium tin oxide nanoparticles, at which whole enzyme cascades are assembled and trapped in the nanopores. The electrochemical leaf provides a powerful new way to synthesise complex organic molecules. The technology, which embodies fast and efficient NAD(P)(H) cofactor recycling within electrode nanocavities, allows biocatalysis to be investigated and exploited with unprecedented ease.
Using sunlight to drive chemical reactions has long been one of the goals in developing sustainable processes. Previous research has focused on solar fuel production in the form of H2, but this ...thesis demonstrates that solar-to-chemicals processes can be constructed to produce more complex compounds, using hybrid systems composed of enzymes and inorganic materials. Tetrachloroethene reductive dehalogenase (PceA), an enzyme that catalyzes the conversion of tetrachloroethene (PCE) to trichloroethene (TCE) and subsequently to cis-dichloroethene (cDCE), was shown to accept electrons from both graphite and TiO2 electrodes. Irradiation by UV light onto PceA-adsorbed TiO2 particles led to the selective production of TCE and cDCE, which was not possible without PceA as a catalyst. Ferredoxin-NADP+ reductase (FNR) is a key enzyme in photosynthesis, as it receives energetic electrons from Photosystem I and produces NADPH as an energy carrier for downstream 'Dark' reactions involving CO2 assimilation. This thesis presents the discovery of FNR activity on indium tin oxide (ITO) electrodes which led to direct electrochemical investigation of the properties of FNR, both in the absence and presence of its substrate, NADP+. The FNR-adsorbed electrode, termed 'the electrochemical leaf', rapidly interconverts NADP+/NADPH, and this was coupled to a downstream NADPH-dependent enzyme, thus demonstrating a new approach to cofactor regeneration for enzyme-catalyzed organic synthesis. The NADP+ reduction by FNR was also driven by light using a photoanode made of visible-light responsive semiconductors.
Using sunlight to drive chemical reactions has long been one of the goals in developing sustainable processes. Previous research has focused on solar fuel production in the form of H2, but this ...thesis demonstrates that solar-to-chemicals processes can be constructed to produce more complex compounds, using hybrid systems composed of enzymes and inorganic materials. Tetrachloroethene reductive dehalogenase (PceA), an enzyme that catalyzes the conversion of tetrachloroethene (PCE) to trichloroethene (TCE) and subsequently to cis-dichloroethene (cDCE), was shown to accept electrons from both graphite and TiO2 electrodes. Irradiation by UV light onto PceA-adsorbed TiO2 particles led to the selective production of TCE and cDCE, which was not possible without PceA as a catalyst. Ferredoxin-NADP+ reductase (FNR) is a key enzyme in photosynthesis, as it receives energetic electrons from Photosystem I and produces NADPH as an energy carrier for downstream 'Dark' reactions involving CO2 assimilation. This thesis presents the discovery of FNR activity on indium tin oxide (ITO) electrodes which led to direct electrochemical investigation of the properties of FNR, both in the absence and presence of its substrate, NADP+. The FNR-adsorbed electrode, termed 'the electrochemical leaf', rapidly interconverts NADP+/NADPH, and this was coupled to a downstream NADPH-dependent enzyme, thus demonstrating a new approach to cofactor regeneration for enzyme-catalyzed organic synthesis. The NADP+ reduction by FNR was also driven by light using a photoanode made of visible-light responsive semiconductors.
Tetrachloroethene reductive dehalogenase (PceA), a corrinoid-containing enzyme from
Sulfurospirillum multivorans
, is highly active for the sequential reduction of the organohalide tetrachloroethene ...(PCE) to trichloroethene (TCE), then regiospecifically to
cis
-1,2-dichloroethene (
c
DCE). We demonstrate direct electron transfer from graphite and semiconductor electrodes to PceA adsorbed onto the electrode surface. Colloidal TiO
2
nanoparticles modified with PceA efficiently carry out the sequence of dehalogenation reactions under UV light irradiation.
In a discovery of the transfer of chloroplast biosynthesis activity to an inorganic material, ferredoxin-NADP
+
reductase (FNR), the pivotal redox flavoenzyme of photosynthetic CO
2
assimilation, ...binds tightly within the pores of indium tin oxide (ITO) to produce an electrode for direct studies of the redox chemistry of the FAD active site, and fast, reversible and diffusion-controlled interconversion of NADP
+
and NADPH in solution. The dynamic electrochemical properties of FNR and NADP(H) are thus revealed in a special way that enables facile coupling of selective, enzyme-catalysed organic synthesis to a controllable power source, as demonstrated by efficient synthesis of
l
-glutamate from 2-oxoglutarate and NH
4
+
.
A bio-hybrid material has been discovered, which offers a new direction for fast, specific enzyme-catalyzed organic synthesis.
A bio-hybrid material has been discovered, which offers a new direction for fast, specific enzyme-catalyzed organic synthesis.
In a discovery of the transfer of chloroplast biosynthesis activity to ...an inorganic material, ferredoxin–NADP
+
reductase (FNR), the pivotal redox flavoenzyme of photosynthetic CO
2
assimilation, binds tightly within the pores of indium tin oxide (ITO) to produce an electrode for direct studies of the redox chemistry of the FAD active site, and fast, reversible and diffusion-controlled interconversion of NADP
+
and NADPH in solution. The dynamic electrochemical properties of FNR and NADP(H) are thus revealed in a special way that enables facile coupling of selective, enzyme-catalysed organic synthesis to a controllable power source, as demonstrated by efficient synthesis of
l
-glutamate from 2-oxoglutarate and NH
4
+
.
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