Catalysts and electrodes for the electroreduction of carbon dioxide to useful chemicals

Industrialization and increasing population have brought the world two major challenges: climate change and increasing energy demands. First, the atmospheric CO2 level has increased to 400 ppm, and already this high level has been associated with undesirable climate effects such as global warming and an increased occurrence of erratic weather. Second, the world faces challenges in meeting its energy needs due to increasing global population as well as the dwindling resources of fossil fuels on the earth. Various strategies such as switching from fossil fuel derived energy to nuclear energy or renewable energy sources (solar, wind, hydro) need to be pursued to curb the increase in atmospheric CO2 levels while decreasing our dependence on fossil fuels. However, due to the lack of efficient ways for large-scale energy storage, significant amounts of renewable energy will be wasted when the supply is higher than the actual demand due to its intermittency. A potential strategy that can be employed to help overcome both challenges is the electroreduction of CO2 into useful feedstock chemicals or fuels such as formic acid, carbon monoxide, hydrocarbons, and alcohols using otherwise wasted large amounts of intermittent excess renewable energy. Although the electroreduction of CO2 offers the potential to recycle CO2 and store intermittent renewable energy, this process is still not economically viable due to insufficient performance levels, specifically due to high overpotentials which reduce energy efficiency, low current densities and low selectivities. Better catalysts that show high activity as well as electrodes that exhibit excellent mass transfer capabilities and electron conductivities are needed. This dissertation reports the development of active and durable catalysts that exhibit low overpotentials for the electroreduction of CO2 to products such as CO, C2H4 and/or C2H5OH. This dissertation will also discuss the roles electrolytes and electrode structures play in the electroreduction of CO2. The focus of Chapters 2 and 3 is on developing better cathode and anode catalysts for the electroreduction of CO2 to CO. Chapter 2 reports on the role of support materials on cathode performance. Ag supported on TiO2 exhibited a twofold higher partial current density for CO than Ag supported on C with the same Ag loading and similar performance compared to unsupported Ag nanoparticles, but at a 2.5 times lower Ag loading. The TiO2 support material was also found to stabilize a reaction intermediate and serves as a redox electron carrier to assist the CO2 reduction reaction. Chapter 3 reports how two forms of IrO2, dihydrate and non-hydrate, improve system energy efficiency and production rate when used as the anode catalyst. For example, when IrO2 dihydrate was used as the anode catalyst instead of platinum black, the energy efficiency increased by 40% and the current density showed a 2-fold improvement. Chapters 4, 5, and 6 focus on developing active Cu-based cathode catalysts for the electroreduction of CO2 to C2 chemicals. Chapter 4 reports the synthesis and application of active Cu nanoparticles with different morphology and composition (amount of surface oxide) for CO2 reduction in an alkaline electrolyzer. The use of catalysts with large surface roughness results in a high Faradaic efficiency of 46% (only ~30% in most prior work) for the conversion of CO2 to C2 chemicals with a total current density of ~200 mA cm-2 for these C2 products, which, compared to prior work, represents a 10-fold increase in conversion rate at much lower overpotential (only < 0.7 V). The effect of N-containing compounds on the products distribution for the electroreduction of CO2 on Cu catalysts is discussed in Chapter 5. Specifically, 3,5-diamino-1,2,4-triazole (DAT) improves the Faradaic efficiency of C2H4 by more than 1.5 fold when used in combinations with a Cu nanoparticle-based electrode. In-situ surface enhanced Raman Spectroscopy (SERS) was applied to elucidate the possible reasons for this improvement. Chapter 6 describes the design, synthesis and application of CuPd nanoalloys with tunable atomic arrangements (atomically ordered, disordered and phase-separated structures) for the electroreduction of CO2 to C2 chemicals. The results of electrochemical measurement as well as structural and compositional characterization indicate that the observed differences in selectivities for different products can be attributed predominantly to structural differences in the different catalysts. Also, this work for the first time shows that active sites with neighboring Cu atoms are required for the efficient conversion of CO2 to C2 chemicals. Finally, Chapter 7 describes the improvement in throughput levels for the electroreduction of CO2 to CO through the optimization of electrode structure and composition. The electrode that incorporates multi-walled carbon nanotubes (MWCNTs) in the catalyst layer achieves high levels of CO production of up to 350 mA cm-2 at a high Faradaic efficiency (>95% selective for CO) and an energy efficiency of 45%. This level of performance represents a twofold improvement over the performance achieved with electrodes that lack MWCNTs. In summary the studies reported in this dissertation provide insight regarding the design and synthesis of active catalysts and electrodes that improve current density (conversion), selectivity and energy efficiency for the electroreduction of CO2 to different chemical intermediates of value

Table 1_v1_Peripheral blood eosinophil and classification of residual hematoma help predict the recurrence of chronic subdural hematoma after initial surgery.docx

Chronic subdural hematoma (CSDH) is a common type of intracranial hemorrhage in neurosurgical practice, whose incidence has increased markedly in recent years. However, CSDH still troubles clinicians with a high postoperative recurrence rate. The presence of eosinophils has been confirmed in some CSDH surgical specimens. Furthermore, postoperative residual hematoma has not been classified, and its association with the recurrence of CSDH remains unknown. The present study aimed to test the hypothesis that the peripheral blood eosinophils and the classification of postoperative residual hematoma are significant for the prediction of CSDH recurrence after burr-hole surgery. A retrospective review of 258 CSDH patients who received burr-hole surgery was performed. A complete blood picture with differential count was taken before surgery. Clinical, laboratory, and radiographic factors predicting CSDH recurrence were identified in univariable and multivariable analyses. Univariable analysis showed that the percentage of eosinophils, peripheral blood eosinophil count 9/L, gradation and separated types, postoperative volume of the residual cavity ≥70 ml, residual air volume ≥28 ml, residual hematoma volume ≥55 ml, residual hematoma width ≥1.4 cm, postoperative midline shift ≥5.6 mm, postoperative brain re-expansion rate 9/L, gradation and separated types, preoperative midline shift ≥9.5 mm, postoperative brain re-expansion rate <41%, postoperative low-density type, and postoperative high-density type are independent predictors for the recurrence of CSDH. We expect that peripheral blood eosinophils and the classification of postoperative residual hematoma may facilitate our understanding of the recurrence of CSDH after initial surgery.</p

The role of klotho in chronic kidney disease

Abstract Chronic kidney disease (CKD) is an inherently systemic disease that refers to a long-term loss of kidney function. The progression of CKD has repercussions for other organs, leading to many kinds of extrarenal complications. Intensive studies are now being undertaken to reveal the risk factors and pathophysiological mechanism of this disease. During the past 20 years, increasing evidence from clinical and basic studies has indicated that klotho, which was initially known as an anti-aging gene and is mainly expressed in the kidney, is significantly correlated with the development and progression of CKD and its complications. Here, we discuss in detail the role and pathophysiological implications of klotho in ion disorders, the inflammation response, vascular calcification, mineral bone disorders, and renal fibrosis in CKD. Based on the pathogenic mechanism of klotho deficiency and klotho decline in urine early in CKD stage 2 and even earlier in CKD stage 1, it is not difficult to understand that soluble klotho can serve as an early and sensitive marker of CKD. Moreover, the prevention of klotho decline by several mechanisms can attenuate renal injuries, retard CKD progression, ameliorate extrarenal complications, and improve renal function. In this review, we focus on the functions and pathophysiological implications of klotho in CKD and its extrarenal complications as well as its potential applications as a diagnostic and/or prognostic biomarker for CKD and as a novel treatment strategy to improve and decrease the burden of comorbidity in CKD

Carbon foam decorated with silver nanoparticles for electrochemical CO2 conversion

Electrochemistry is a promising method to recycle CO2 into useful carbon feedstock and for storing intermittent renewable energy. To date, Au and Ag nanoparticles are the most active catalysts for electrochemical conversion of CO2 to CO. However, agglomeration reduces the activity and the high cost slows widespread commercialization. Suitable support materials are thus needed to improve catalyst utilization. We explore carbon foam (CF) as a catalyst support. Compared with carbon black or graphene nanoplatelets, CF has higher surface area, larger pores, and more defects, resulting in improved uniformity of Ag nanoparticle distribution as well as higher activity and efficiency for CO2 conversion to CO

A sensitive flow-batch system for on board determination of ultra-trace ammonium in seawater: Method development and shipboard application

Science Fund for Creative Research Groups of the National Natural Science Foundation of China [41121091]; China National Basic Research Program ("973" Program) "Carbon cycling in China Seas-budget, controls and ocean acidification (CHOICE-C Project)" [2009CB421200]Combining fluorescence detection with flow analysis and solid phase extraction (SPE), a highly sensitive and automatic flow system for measurement of ultra-trace ammonium in open ocean water was established. Determination was based on fluorescence detection of a typical product of o-phthaldialdehyde and ammonium. In this study, the fluorescence reaction product could be efficiently extracted onto an SPE cartridge (HLB, hydrophilic-lipophilic balance). The extracted fluorescence compounds were rapidly eluted with ethanol and directed into a flow cell for fluorescence detection. Compared with the common used fluorescence method, the proposed one offered the benefits of improved sensitivity, reduced reagent consumption, negligible salinity effect and lower cost. Experimental parameters were optimized using a univariate experimental design. Calibration curves, ranging from 1.67 to 300 nM, were obtained with different reaction times. The recoveries were between 89.5 and 96.5%, and the detection limits in land-based and shipboard laboratories were 0.7 and 1.2 nM, respectively. The relative standard deviation was 3.5% (n = 5) for an aged seawater sample spiked with 20 nM ammonium. Compared with the analytical results obtained using the indophenol blue method coupled to a long-path liquid waveguide capillary cell, the proposed method showed good agreement. The method had been applied on board during a South China Sea cruise in August 2012. A vertical profile of ammonium in the South East Asia Time-Series (SEATS, 18 degrees N, 116 degrees E) station was produced. The distribution of ammonium in the surface seawater of the Qiongdong upwelling in South China Sea is also presented. (C) 2013 Elsevier B. V. All rights reserved

A modified method for on-line determination of trace ammonium in seawater with a long-path liquid waveguide capillary cell and spectrophotometric detection

Science Fund for Creative Research Groups of the National Natural Science Foundation of China [41121091]An automated calorimetric method for the on-line determination of trace ammonium in seawater was established using a flow injection technique coupled with a 2.5-m liquid waveguide capillary cell. Using low ammonium seawater as a carrier, a sample was injected into the carrier and mixed with reagents to form indophenol blue dye, which was monitored at a wavelength of 690 nm. Different strategies of reagent injection were investigated to obtain a lower reagent blank and a higher detection sensitivity. Experimental parameters were optimized using a univariate experimental design, and the matrix effect of seawater was preliminarily investigated. The proposed method had high sensitivity with a detection limit of 3.6 nmol.L-1. The linearity was 10 to 500 nmol.L-1 and the upper limit could be extended to 30 mu mol.L-1 by choosing a less sensitive detection wavelength or lower reaction temperature. The recoveries were between 95.0 and 104.3% and the relative standard deviation was 4.4% (n = 7) for an aged seawater sample spiked with 50 nmol.L-1 ammonium. The sample throughput was 22 h(-1). The analytical results obtained with the proposed method showed good agreement with those using reference fluorescence methods. Compared with the normal indophenol blue (off-line) method, the proposed method was superior due to its lower reagent consumption, greater convenience, higher sample throughput, wider linear range (10 nmol.L-1 to 30 mu mol.L-1), as well as higher sensitivity. The method was applied in-field in Wuyuan Bay for 24 h on-line monitoring of ammonium concentrations in the surface seawater. In addition, it was also used to analyze surface seawater samples collected from the South China Sea for the study of ammonium distribution. (C) 2014 Elsevier B.V. All rights reserved

Effects of Applying Different Organic Materials on Grain Yield and Soil Fertility in a Double-Season Rice Cropping System

Double-cropping rice cultivation reduces soil fertility, and the extensive use of chemical fertilizers has harmful effects on both the environment and grain yield. The application of organic materials could be used as a practical strategy to maintain soil fertility and improve grain yield in a double-season rice cropping system. For this purpose, field experiments with six growing seasons over three years, from 2016 to 2018, were conducted to assess the effects of five organic materials (biochar, Chinese milk vetch, rice straw, rapeseed cake fertilizer, and manure) on the grain yield and soil fertility, aiming to save about 25% of the chemical nitrogen (N) fertilizer required for all rice growing stages. The result showed that, compared with CK (the most common dose of fertilizer in this study region; 100% chemical fertilizer without organic fertilizer), the grain yield and soil fertility of double-cropped rice were increased after applying organic fertilizers for three consecutive years. Specifically, the CRC treatment (Chinese milk vetch (10.77 t ha&minus;1 in fresh)/rice straw (26.51 t ha&minus;1 in fresh) + 75% chemical fertilizer) showed significantly higher rates of effective panicles (4.65&ndash;10.92%) and annual grain yield (8.00&ndash;8.82%). The total N, total phosphorus (P), total potassium (K), alkaline N, and available P content in the CRC soil were significantly increased by 11.85%, 12.22%, 15.08%, 23.32%, and 41.04%, respectively, relative to CK. The decomposition of the applied Chinese milk vetch and rice straw combined with 75% chemical fertilizer resulted in more soil humus (9.50 g kg&minus;1), humic acid (3.19 g kg&minus;1), fulvic acid (3.26 g kg&minus;1), and active organic carbon (5.78 g kg&minus;1) and a significantly higher carbon pool management index (13.5%), as well as significantly higher soil urease activity (18.10%) and acid phosphatase activity (17.64%). Therefore, in this study, Chinese milk vetch (10.77 t ha&minus;1 in fresh) in the early rice season/rice straw (26.51 t ha&minus;1 fresh) in the late rice season + 75% chemical fertilizer treatment was the optimal dose for the double-season rice cropping system. It resulted in higher rice yields and has the potential to be used for more sustainable soil fertility

High-sensitivity, selective determination of dopamine using bimetallic nanoparticles modified boron-doped diamond electrode with anodic polarization treatment

Selective detection of dopamine is still a challenge due to the strong interference from ascorbic acid (AA). A hybrid dopamine electrochemical sensor was fabricated by boron-doped diamond (BDD) film co-modified with gold nanoparticles and graphite-coated nickel nanoparticles (Au-C@Ni/BDD). Highly sensitive and selective detection toward dopamine was achieved by multiple electrochemical anodic polarization treatment (EAPT) with relatively mild voltage (+ 1.6 V vs. Ag/AgCl) on Au-C@Ni/BDD electrode. Specifically, the oxidation peak separation between ascorbic acid and dopamine reached 166 mV, and the limit of detection of dopamine was as low as 0.015 μM in a linear concentration range of 0.05–100 μM with the sensitivity up to 1.99 μA μM−1 cm−2 even in the presence of interference of high-level AA. These could be ascribed to the electrocatalytically active sites and functional oxygen-containing groups of the hybrid electrodes produced by the EAPT and the excellent catalytical activity of gold nanoparticles

Nitrogen-Based Catalysts for the Electrochemical Reduction of CO₂ to CO

The synthesis and application of carbon-supported, nitrogen-based organometallic silver catalysts for the reduction of CO₂ is studied using an electrochemical flow reactor. Their performance toward the selective formation of CO is similar to the performance achieved when using Ag as the catalyst, but comparatively at much lower silver loading. Faradaic efficiencies of the organometallic catalyst are higher than 90%, which are comparable to those of Ag. Furthermore, with the addition of an amine ligand to Ag/C, the partial current density for CO increases significantly, suggesting a possible co-catalyst mechanism. Additional improvements in activity and selectivity may be achieved as greater insight is obtained on the mechanism of CO₂ reduction and on how these complexes assemble on the carbon support