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CURATOR
A pinboard by
Nikolay Kornienko

Postdoctoral Researcher, University of Cambridge

PINBOARD SUMMARY

Developing the technologies for a cleaner tomorrow

My overarching motivation is to discover and implement the chemistry necessary to transition to a sustainable energy-based society. Specifically, I am developing materials to convert solar energy to chemical fuels as an energy storage media. Transforming solar energy into chemical bonds requires efficient, synchronous function of multiple processes as well as a fundamental understanding of the underlying chemistry at work. Currently, catalysts that utilize solar-derived electricity to generate chemical fuels lack the performance necessary to render this technology practical. Within this framework, my research entails both the design of novel electrocatalytic materials and in situ spectroscopic investigations. The aim here is to establish an iterative cycle where novel materials are first synthesized and systematically tested then subsequently probed through spectroscopic methods to develop a comprehensive understanding of the materials' structure/function relationships. The lessons generated can then be feed into the next cycle of design, synthesis, and understanding to accelerate the rate at which the pressing challenges in energy and materials can be met.

My present research entails the applications of electroanalytical methodology combined with in situ spectroscopic approaches towards developing a comprehensive understanding of enzymatic catalysts. Specifically, I am probing the structure-function relationships of Photosystem II, the component responsible for absorbing light and oxidizing water in photosynthesis. The primary motivation for this line of research is do understand how Photosystem II, as a model system, performs solar-driven water oxidation with such high efficiency, and utilize these findings to improve man-made water oxidizing systems.

19 ITEMS PINNED

Spectroscopic elucidation of energy transfer in hybrid inorganic-biological organisms for solar-to-chemical production.

Abstract: The rise of inorganic-biological hybrid organisms for solar-to-chemical production has spurred mechanistic investigations into the dynamics of the biotic-abiotic interface to drive the development of next-generation systems. The model system, Moorella thermoacetica-cadmium sulfide (CdS), combines an inorganic semiconductor nanoparticle light harvester with an acetogenic bacterium to drive the photosynthetic reduction of CO2 to acetic acid with high efficiency. In this work, we report insights into this unique electrotrophic behavior and propose a charge-transfer mechanism from CdS to M. thermoacetica Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates increase with increasing hydrogenase (H2ase) enzyme activity. On the same time scale as the TA spectroscopy, time-resolved infrared (TRIR) spectroscopy showed spectral changes in the 1,700-1,900-cm(-1) spectral region. The quantum efficiency of this system for photosynthetic acetic acid generation also increased with increasing H2ase activity and shorter carrier lifetimes when averaged over the first 24 h of photosynthesis. However, within the initial 3 h of photosynthesis, the rate followed an opposite trend: The bacteria with the lowest H2ase activity photosynthesized acetic acid the fastest. These results suggest a two-pathway mechanism: a high quantum efficiency charge-transfer pathway to H2ase generating H2 as a molecular intermediate that dominates at long time scales (24 h), and a direct energy-transducing enzymatic pathway responsible for acetic acid production at short time scales (3 h). This work represents a promising platform to utilize conventional spectroscopic methodology to extract insights from more complex biotic-abiotic hybrid systems.

Pub.: 05 Oct '16, Pinned: 22 Jun '17

Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex.

Abstract: The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni((Pr)bimiq1)](2+) (1c, where (Pr)bimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (E(cat) = -1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s(-1), respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

Pub.: 17 Sep '13, Pinned: 22 Jun '17

Atomic Structure of Pt3Ni Nanoframe Electrocatalysts by in Situ X-ray Absorption Spectroscopy

Abstract: Understanding the atomic structure of a catalyst is crucial to exposing the source of its performance characteristics. It is highly unlikely that a catalyst remains the same under reaction conditions when compared to as-synthesized. Hence, the ideal experiment to study the catalyst structure should be performed in situ. Here, we use X-ray absorption spectroscopy (XAS) as an in situ technique to study Pt3Ni nanoframe particles which have been proven to be an excellent electrocatalyst for the oxygen reduction reaction (ORR). The surface characteristics of the nanoframes were probed through electrochemical hydrogen underpotential deposition and carbon monoxide electrooxidation, which showed that nanoframe surfaces with different structure exhibit varying levels of binding strength to adsorbate molecules. It is well-known that Pt-skin formation on Pt–Ni catalysts will enhance ORR activity by weakening the binding energy between the surface and adsorbates. Ex situ and in situ XAS results reveal that nanoframes which bind adsorbates more strongly have a rougher Pt surface caused by insufficient segregation of Pt to the surface and consequent Ni dissolution. In contrast, nanoframes which exhibit extremely high ORR activity simultaneously demonstrate more significant segregation of Pt over Ni-rich subsurface layers, allowing better formation of the critical Pt-skin. This work demonstrates that the high ORR activity of the Pt3Ni hollow nanoframes depends on successful formation of the Pt-skin surface structure.

Pub.: 10 Dec '15, Pinned: 22 Jun '17

Single-nanowire photoelectrochemistry

Abstract: Photoelectrochemistry1, 2, 3 is one of several promising approaches4, 5 for the realization of efficient solar-to-fuel conversion. Recent work has shown that photoelectrodes made of semiconductor nano-/microwire arrays can have better photoelectrochemical performance6, 7, 8 than their planar counterparts because of their unique properties, such as high surface area9, 10, 11. Although considerable research effort has focused on studying wire arrays, the inhomogeneity in the geometry, doping, defects and catalyst loading present in such arrays can obscure the link between these properties and the photoelectrochemical performance of the wires, and correlating performance with the specific properties of individual wires is difficult because of ensemble averaging. Here, we show that a single-nanowire-based photoelectrode platform can be used to reliably probe the current–voltage (I–V) characteristics of individual nanowires. We find that the photovoltage output of ensemble array samples can be limited by poorly performing individual wires, which highlights the importance of improving nanowire homogeneity within an array. Furthermore, the platform allows the flux of photogenerated electrons to be quantified as a function of the lengths and diameters of individual nanowires, and we find that the flux over the entire nanowire surface (7–30 electrons nm–2 s–1) is significantly reduced as compared with that of a planar analogue (∼1,200 electrons nm–2 s–1). Such characterization of the photogenerated carrier flux at the semiconductor/electrolyte interface is essential for designing nanowire photoelectrodes that match the activity of their loaded electrocatalysts.

Pub.: 28 Mar '16, Pinned: 22 Jun '17