Nathan S. Lewis

Bio: Nathan S. Lewis is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Semiconductor & Silicon. The author has an hindex of 112, co-authored 720 publications receiving 64808 citations. Previous affiliations of Nathan S. Lewis include Lawrence Berkeley National Laboratory & Massachusetts Institute of Technology.

Proton exchange membrane electrolysis sustained by water vapor

Abstract: The current–voltage characteristics of a proton exchange membrane (PEM) electrolyzer constructed with an IrRuOx water oxidation catalyst and a Pt black water reduction catalyst, under operation with water vapor from a humidified carrier gas, have been investigated as a function of the gas flow rate, the relative humidity, and the presence of oxygen. The performance of the system with water vapor was also compared to the performance when the device was immersed in liquid water. With a humidified Ar(g) input stream at 20 °C, an electrolysis current density of 10 mA cm−2 was sustained at an applied voltage of ∼1.6 V, with a current density of 20 mA cm−2 observed at ∼1.7 V. In the system evaluated, at current densities >40 mA cm−2 the electrolysis of water vapor was limited by the mass flux of water to the PEM. At <40 mA cm−2, the electrolysis of water vapor supported a given current density at a lower applied bias than did the electrolysis of liquid water. The relative humidity of the input carrier gas strongly affected the current–voltage behavior, with lower electrolysis current density attributed to dehydration of the PEM at reduced humidity values. The results provide a proof-of-concept that, with sufficiently active catalysts, an efficient solar photoelectrolyzer could be operated only with water vapor as the feedstock, even at the low operating temperatures that may result in the absence of active heating. This approach therefore offers a route to avoid the light attenuation and mass transport limitations that are associated with bubble formation in these systems.

The Influence of Structure and Processing on the Behavior of TiO2 Protective Layers for Stabilization of n-Si/TiO2/Ni Photoanodes for Water Oxidation

Abstract: Light absorbers with moderate band gaps (1–2 eV) are required for high-efficiency solar fuels devices, but most semiconducting photoanodes undergo photocorrosion or passivation in aqueous solution. Amorphous TiO2 deposited by atomic-layer deposition (ALD) onto various n-type semiconductors (Si, GaAs, GaP, and CdTe) and coated with thin films or islands of Ni produces efficient, stable photoanodes for water oxidation, with the TiO2 films protecting the underlying semiconductor from photocorrosion in pH = 14 KOH(aq). The links between the electronic properties of the TiO2 in these electrodes and the structure and energetic defect states of the material are not yet well-elucidated. We show herein that TiO2 films with a variety of crystal structures and midgap defect state distributions, deposited using both ALD and sputtering, form rectifying junctions with n-Si and are highly conductive toward photogenerated carriers in n-Si/TiO2/Ni photoanodes. Moreover, the photovoltage of these electrodes can be modified...

Electrolysis of water at strontium titanate (SrTiO3) photoelectrodes: distinguishing between the statistical and stochastic formalisms for electron-transfer processes in fuel-forming photoelectrochemical systems

Abstract: Conventional photoelectrochemical and photovoltaic theory predicts a light intensity threshold for sustaining the net electrolysis of water using semiconductor electrodes, but a stochastic charge-transfer formalism for photoelectrolysis reactions does not predict such threshold behavior.

In situ recombination junction between p-Si and TiO2 enables high-efficiency monolithic perovskite/Si tandem cells.

Abstract: Increasing the power conversion efficiency of silicon (Si) photovoltaics is a key enabler for continued reductions in the cost of solar electricity. Here, we describe a two-terminal perovskite/Si tandem design that increases the Si cell’s output in the simplest possible manner: by placing a perovskite cell directly on top of the Si bottom cell. The advantageous omission of a conventional interlayer eliminates both optical losses and processing steps and is enabled by the low contact resistivity attainable between n-type TiO2 and Si, established here using atomic layer deposition. We fabricated proof-of-concept perovskite/Si tandems on both homojunction and passivating contact heterojunction Si cells to demonstrate the broad applicability of the interlayer-free concept. Stabilized efficiencies of 22.9 and 24.1% were obtained for the homojunction and passivating contact heterojunction tandems, respectively, which could be readily improved by reducing optical losses elsewhere in the device. This work highlights the potential of emerging perovskite photovoltaics to enable low-cost, high-efficiency tandem devices through straightforward integration with commercially relevant Si solar cells.

Colloidal particles used in sensing arrays

Abstract: Chemical sensors for detecting analytes in fluids comprising a plurality of alternating nonconductive regions (comprising a nonconductive material) and conductive regions (comprising a conductive material). In preferred embodiments, the conducting region comprises a nanoparticle. Variability in chemical sensitivity from sensor to sensor is provided by qualitatively or quantitatively varying the composition of the conductive and/or nonconductive regions. An electronic nose for detecting an analyte in a fluid may be constructed by using such arrays in conjunction with an electrical measuring device electrically connected to the conductive elements of each sensor.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Heterogeneous photocatalyst materials for water splitting

Abstract: This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials Photocatalytic water splitting and H2 evolution using abundant compounds as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen production, and a solution of global energy and environmental issues in the future (361 references)