Electrochemical Approaches toward CO2 Capture and Concentration

Carbon capture and concentration of low partial pressure CO2 in air and flue gas is a key step in carbon abatement strategies. Traditional CO2 capture methods employ temperature or pressure swings, however electrochemical swings, in which an applied potential modulates nucleophilicity, are also possible to mediate the capture and release of CO2. In contrast to the breadth of electrochemical CO2 reduction research, electrochemically mediated CO2 capture and concentration is an emerging field. Although some aspects are reminiscent to those in CO2 reduction, like local pH gradients and bi carbonate equilibria, ultimately electrochemical CO2 capture and concentration poses its own unique challenges that will benefit from insights from intercalative batteries, redox flow batteries, and bio mimetic inspired design, among others. After an introduction to carbon capture and current chemical strategies, this review highlights promising emerging electrochemical methods to enable CO2 capture and concentration; specifically discussed are transition metal redox and pH swings. It closes with an outlook and discussion of future research challenge

Light Induced Surface Reactions at the Bismuth Vanadate Potassium Phosphate Interface

Bismuth vanadate has recently drawn significant research attention as a light absorbing photoanode due to its performance for photoelectrochemical water splitting. In this study, we use in situ ambient pressure X ray photoelectron spectroscopy with Tender X rays 4.0 keV to investigate a polycrystalline bismuth vanadate BiVO4 electrode in contact with an aqueous potassium phosphate KPi solution at open circuit potential under both dark and light conditions. This is facilitated by the creation of a 25 to 30 nanometers thick electrolyte layer using the dip and pull method. We observe that under illumination bismuth phosphate forms on the BiVO4 surface leading to an increase of the surface negative charge. The bismuth phosphate layer may act to passivate surface states observed in photoelectrochemical measurements. The repulsive interaction between the negatively charged surface under illumination and the phosphate ions in solution causes a shift in the distribution of ions in the thin aqueous electrolyte film, which is observed as an increase in their photoelectron signals. Interestingly, we find that such changes at the BiVO4 KPi electrolyte interface are reversible upon returning to dark conditions. By measuring the oxygen 1s photoelectron peak intensities from the phosphate ions and liquid water as a function of time under dark and light conditions, we determine the timescales for the forward and reverse reactions. Our results provide direct evidence for light induced chemical modification of the BiVO4 KPi electrolyte interfac

Enhanced Carrier Transport and Bandgap Reduction in Sulfur Modified BiVO4 Photoanodes

Recent progress on bismuth vanadate BiVO4 has shown it to be among the highest performing metal oxide photoanode materials. However, further improvement, especially in the form of thin film photoelectrodes, is hampered by its poor charge carrier transport and its relatively wide bandgap. Here, sulfur incorporation is used to address these limitations. A maximum bandgap decrease of 0.3 eV is obtained, which increases the theoretical maximum solar to hydrogen efficiency from 9 to 12 . Hard X ray photoelectron spectroscopy HAXPES measurements as well as density functional theory DFT calculations show that the main reason for the bandgap decrease is an upward shift of the valence band maximum. Time resolved microwave conductivity measurements reveal an 3 times higher charge carrier mobility compared to unmodified BiVO4, resulting in a 70 increase in the carrier diffusion length. This work demonstrates that sulfur doping can be a promising and practical method to improve the performance of wide bandgap metal oxide photoelectrode

Quantification of the Activator and Sensitizer Ion Distributions in NaYF4 Yb3 , Er3 Upconverting Nanoparticles Via Depth Profiling with Tender X Ray Photoemission

The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles UCNPs . Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X ray photoelectron spectroscopy depth profiling with tender X rays 2000 6000 eV , providing probe depths ideally matched to UCNP sizes, is used to measure the depth dependent concentration ratios of Er3 to Yb3 , [Er3 ] [Yb3 ], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma optical emission spectroscopy ICP OES measurements of the lanthanide ion concentrations to construct models of the UCNPs dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core only UCNPs synthesized with XCl3 6H2O precursors amp; 946; phase exhibit a homogeneous distribution of lanthanide ions, but a slightly surface enhanced [Er3 ] [Yb3 ] is observed for UCNPs prepared with trifluroacetate precursors amp; 945; phase . Examination of Yb core Er shell UCNPs reveals a co doped, intermixed region between the single doped core and shell. The impact of these different dopant ion distributions on the UCNP s optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNP

Influence of Excess Charge on Water Adsorption on the BiVO4 010 Surface

We present a combined computational and experimental study of the adsorption of water on the Mo doped BiVO4 010 surface, revealing how excess electrons influence the dissociation of water and lead to hydroxyl induced alterations of the surface electronic structure. By comparing ambient pressure resonant photoemission spectroscopy AP ResPES measurements with the results of first principles calculations, we show that the dissociation of water on the stoichiometric Mo doped BiVO4 010 surface stabilizes the formation of a small electron polaron on the VO4 tetrahedral site and leads to an enhanced concentration of localized electronic charge at the surface. Our calculations demonstrate that the dissociated water accounts for the enhanced V4 signal observed in ambient pressure X ray photoelectron spectroscopy and the enhanced signal of a small electron polaron inter band state observed in AP ResPES measurements. For ternary oxide surfaces, which may contain oxygen vacancies in addition to other electron donating dopants, our study reveals the importance of defects in altering the surface reactivity toward water and the concomitant water induced modifications to the electronic structur

Interfacial Oxide Formation Limits the Photovoltage of Alpha SnWO4 NiOx Photoanodes Prepared by Pulsed Laser Deposition

alpha SnWO4 is a promising metal oxide photoanode material for direct photoelectrochemical water splitting. With a band gap of 1.9 eV, it ideally matches the requirements as a top absorber in a tandem device theoretically capable of achieving solar to hydrogen STH efficiencies above 20 . It suffers from photoelectrochemical instability, but NiOx protection layers have been shown to help overcome this limitation. At the same time, however, such protection layers seem to reduce the photovoltage that can be generated at the solid electrolyte junction. In this study, an extensive analysis of the alpha SnWO4 NiOx interface is performed by synchrotron based hard X ray photoelectron spectroscopy HAXPES . NiOx deposition introduces a favorable upwards band bending, but also oxidizes Sn2 to Sn4 at the interface. By combining the HAXPES data with open circuit potential OCP analysis, density functional theory DFT calculations, and Monte Carlo based photoemission spectra simulation using SESSA, the presence of a thin oxide layer at the alpha SnWO4 NiOx interface is suggested and shown to be responsible for the limited photovoltage. Based on this new found understanding, suitable mitigation strategies can be proposed. Overall, this study demonstrates the complex nature of solid state interfaces in multi layer photoelectrodes, which needs to be unraveled to design efficient heterostructured photoelectrodes for solar water splittin

EMIL The energy materials in situ laboratory Berlin a novel characterization facility for photovoltaic and energy materials

A knowledge based approach towards developing a new generation of solar energy conversion devices requires a fast and direct feedback between sophisticated analytics and state of the art processing test facilities for all relevant material classes. A promising approach is the coupling of synchrotron based X ray characterization techniques, providing the unique possibility to map the electronic and chemical structure of thin layers and interface regions with relevant in system in situ sample preparation or in operando analysis capabilities in one dedicated laboratory. EMIL, the Energy Materials In situ Laboratory Berlin, is a unique facility at the BESSY II synchrotron light source. EMIL will be dedicated to the in system, in situ, and in operando X ray analysis of materials and devices for energy conversion and energy storage technologies including photovoltaic applications and photo electrochemical processes. EMIL comprises up to five experimental end stations, three of them can access X rays in an energy range of 80 eV 10 keV. For example, one key setup of EMIL combines a suite of advanced spectroscopic characterization tools with industry relevant deposition facilities in one integrated ultra high vacuum system. These deposition tools allow the growth of PV devices based on silicon, compound semiconductors, hybrid heterojunctions, and organo metal halide perovskites on up to 6 sized substrates. EMIL will serve as a research platform for national and international collaboration in the field of photovoltaic photocatalytic energy conversion and beyond. In this paper, we will provide an overview of the analytic and material capabilities at EMIL

Oxidation of Aqueous Phosphorous Acid Electrolyte in Contact with Pt Studied by X ray Photoemission Spectroscopy

The oxidation of the aqueous H3PO3 in contact with Pt was investigated for a fundamental understanding of the Pt aqueous H3PO3 interaction with the goal of providing a comprehensive basis for the further optimization of high temperature polymer electrolyte membrane fuel cells HT PEMFCs . Ion exchange chromatography IEC experiments suggested that in ambient conditions, Pt catalyzes H3PO3 oxidation to H3PO4 with H2O. X ray photoelectron spectroscopy XPS on different substrates, including Au and Pt, previously treated in H3PO3 solutions was conducted to determine the catalytic abilities of selected metals toward H3PO3 oxidation. In situ ambient pressure hard X ray photoelectron spectroscopy AP HAXPES combined with the dip and pull method was performed to investigate the state of H3PO3 at the Pt H3PO3 interface and in the bulk solution. It was shown that whereas H3PO3 remains stable in the bulk solution, the catalyzed oxidation of H3PO3 by H2O to H3PO4 accompanied by H2 generation occurs in contact with the Pt surface. This catalytic process likely involves H3PO3 adsorption at the Pt surface in a highly reactive pyramidal tautomeric configuratio

GWAS analysis of handgrip and lower body strength in older adults in the CHARGE consortium

Decline in muscle strength with aging is an important predictor of health trajectory in the elderly. Several factors, including genetics, are proposed contributors to variability in muscle strength. To identify genetic contributors to muscle strength, a meta-analysis of genomewide association studies of handgrip was conducted. Grip strength was measured using a handheld dynamometer in 27 581 individuals of European descent over 65 years of age from 14 cohort studies. Genomewide association analysis was conducted on ~2.7 million imputed and genotyped variants (SNPs). Replication of the most significant findings was conducted using data from 6393 individuals from three cohorts. GWAS of lower body strength was also characterized in a subset of cohorts. Two genomewide significant (P-value< 5 × 10−8) and 39 suggestive (P-value< 5 × 10−5) associations were observed from meta-analysis of the discovery cohorts. After meta-analysis with replication cohorts, genomewide significant association was observed for rs752045 on chromosome 8 (β = 0.47, SE = 0.08, P-value = 5.20 × 10−10). This SNP is mapped to an intergenic region and is located within an accessible chromatin region (DNase hypersensitivity site) in skeletal muscle myotubes differentiated from the human skeletal muscle myoblasts cell line. This locus alters a binding motif of the CCAAT/enhancer-binding protein-β (CEBPB) that is implicated in muscle repair mechanisms. GWAS of lower body strength did not yield significant results. A common genetic variant in a chromosomal region that regulates myotube differentiation and muscle repair may contribute to variability in grip strength in the elderly. Further studies are needed to uncover the mechanisms that link this genetic variant with muscle strength

Meta-analysis of Genome-Wide Association Studies for Extraversion: Findings from the Genetics of Personality Consortium

Extraversion is a relatively stable and heritable personality trait associated with numerous psychosocial, lifestyle and health outcomes. Despite its substantial heritability, no genetic variants have been detected in previous genome-wide association (GWA) studies, which may be due to relatively small sample sizes of those studies. Here, we report on a large meta-analysis of GWA studies for extraversion in 63,030 subjects in 29 cohorts. Extraversion item data from multiple personality inventories were harmonized across inventories and cohorts. No genome-wide significant associations were found at the single nucleotide polymorphism (SNP) level but there was one significant hit at the gene level for a long non-coding RNA site (LOC101928162). Genome-wide complex trait analysis in two large cohorts showed that the additive variance explained by common SNPs was not significantly different from zero, but polygenic risk scores, weighted using linkage information, significantly predicted extraversion scores in an independent cohort. These results show that extraversion is a highly polygenic personality trait, with an architecture possibly different from other complex human traits, including other personality traits. Future studies are required to further determine which genetic variants, by what modes of gene action, constitute the heritable nature of extraversion