Efficient Electrosynthesis of Hydrogen Peroxide Using Oxygen-Doped Porous Carbon Catalysts at Industrial Current Densities.

Metal-free carbon catalysts (MFCCs) are one of the commonly used catalysts for electrocatalytic two-electron oxygen reduction (2e- ORR) synthesis of hydrogen peroxide (H2O2). Oxygen doping is an effective means to improve the performance of MFCCs, but the performance of oxygen-doped carbon catalysts is still not high enough, and the contribution of different oxygen functional groups (OFGs) to the catalytic performance is still inconclusive. In this paper, carbon-based catalysts with different oxygen contents and ratios of OFGs were prepared, and the high 2e- ORR activity of COOH + C-OH was demonstrated by combining the results of experiments and theoretical calculations. The prepared oxygen-doped carbon-based catalyst C-0.1M80 achieved an onset potential of 0.795 V (vs RHE), a selectivity of up to 98.2% (0.6 V vs RHE), and a H2O2 oxidation current of 1.33 mA cm-2 (0.5 V vs RHE) in a rotating ring-disk electrode test (0.1 M KOH solution), which was an outstanding performance in MFCCs. In a solid electrolyte flow cell, C-0.1M80 achieved a Faraday efficiency of 97.5% at 200 mA cm-2 with a corresponding H2O2 production rate of 123.7 mg cm-2 h-1. In addition, a flow cell stability test was performed at an industrial current density (100 mA cm-2) with an astounding 200 h of uninterrupted operation, also achieving an outstanding average Faradaic efficiency (95.8%).

Novel Nafion/Graphitic Carbon Nitride Nanosheets Composite Membrane for Steam Electrolysis at 110 °C.

Hydrogen is expected to have an important role in future energy systems; however, further research is required to ensure the commercial viability of hydrogen generation. Proton exchange membrane steam electrolysis above 100 °C has attracted significant research interest owing to its high electrolytic efficiency and the potential to reduce the use of electrical energy through waste heat utilization. This study developed a novel composite membrane fabricated from graphitic carbon nitride (g-C3N4) and Nafion and applied it to steam electrolysis with excellent results. g-C3N4 is uniformly dispersed among the non-homogeneous functionalized particles of the polymer, and it improves the thermostability of the membranes. The amino and imino active sites on the nanosheet surface enhance the proton conductivity. In ultrapure water at 90 °C, the proton conductivity of the Nafion/0.4 wt.% g-C3N4 membrane is 287.71 mS cm-1. Above 100 °C, the modified membranes still exhibit high conductivity, and no sudden decreases in conductivity were observed. The Nafion/g-C3N4 membranes exhibit excellent performance when utilized as a steam electrolyzer. Compared with that of previous studies, this approach achieves better electrolytic behavior with a relatively low catalyst loading. Steam electrolysis using a Nafion/0.4 wt.% g-C3N4 membranes achieves a current density of 2260 mA cm-2 at 2 V, which is approximately 69% higher than the current density achieved using pure Nafion membranes under the same conditions.

Low-Loading and Highly Stable Membrane Electrode Based on an Ir@WOxNR Ordered Array for PEM Water Electrolysis.

Developing cheap and stable membrane electrode assembly for proton exchange membrane water electrolysis (PEMWE) plays critical roles in renewable energy revolution. Iridium is the commonly efficient oxygen evolution reaction catalyst. But the reserve in earth is a shortage. Herein, an ordered array electrode in feature of the defective Ir film decorated on external WOx nanorods (WOxNRs) is designed. Electrodeposition is carried out to prepare an iridium coating (∼68 nm in thickness) to guarantee the ordered morphology. This novel electrode obtained brilliant I-V performances (2.2 A cm-2@2.0 V) and 1030 h stability (0.5 mA cm-2) with a reduced loading of 0.14 mgIr cm-2. The uniform dispersion Ir catalyst on the WOx substrate benefits to enhance Ir mass activity and improve the poor conductivity originating from WOx. Compared with that of sprayed electrode, the threshold current density of mass transport polarization region can be expande to at least 3.0 A cm-2 for ordered structure electrode attributed to the abundant water storage bulk. This novel Ir@WOxNRs electrode occupies a huge potential to defuse the cost and durability issues confronting with the PEMWE.

Enzyme-like catalysis of polyoxometalates for chemiluminescence: Application in ultrasensitive detection of H2O2 and blood glucose.

We show that vanadomolybdophosphoric heteropoly acid (H5PMo10V2O40, PMoV2), one of the polyoxometalates (POMs), presents peroxidase-like activity that can catalyze the luminol/H2O2 reaction to generate chemiluminescence (CL) emission. Based on this foundation, we report an enzyme-free luminol/H2O2/PMoV2 CL system that can be utilized for the ultrasensitive detection of H2O2. The CL intensity exhibits good linear dependence on H2O2 concentration in a wide range up to 5000 nM with a limit-of-detection of 5 nM. The method was successfully used for the determination of glucose in human serum. Our study paves the way for the application of functional POM materials in a variety of biosensing assays, such as the determination of cholesterol, uric acid, lactate, etc., in which H2O2 is a product of oxidoreductase enzymes.

Facile synthesis of Pt-decorated Ir black as a bifunctional oxygen catalyst for oxygen reduction and evolution reactions.

Pt-Decorated Ir black (Pt@Ir) nanoparticles with two varying Pt mass fractions (Pt4@Ir96 and Pt16@Ir84) were generated by a facile method in water with the aid of Ir black. The Pt@Ir nanoparticles were investigated as a bifunctional oxygen catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in acidic medium. Benefiting from the good dispersion of ultrafine Pt nanodots on the Ir black surface and the synergistic effect between the Pt and underlying Ir atoms, Pt@Ir nanoparticles have exhibited outstanding ORR activity and comparable OER performance in comparison with commercial Ir black. In particular, Pt16@Ir84 shows an ORR mass activity of 2.6 times that of commercial Pt black and exhibits much better bifunctional performances than a mixture of Pt black and Ir black with a Ir/Pt mass ratio of 50/50 (Pt50Ir50). Our work highlights the effectiveness of decorating Ir black with Pt nanodots to fabricate bifunctional oxygen catalysts.

Highly uniform porous silica layer open-tubular capillary columns produced via in-situ biphasic sol-Gel processing for open-tubular capillary electrochromatography.

We report a highly uniform porous layer open tubular (PLOT) column for capillary electrochromatography (CEC) analysis. The PLOT column is easily fabricated using a single-step in-situ biphasic reaction, producing homogeneous porous-layer modified surface with ∼240 nm thickness in a 50 µm-id capillary. CEC performance of the PLOT column has been investigated and optimized under various experimental parameters. Using a mixture of naphthalene and biphenyl as the test sample, we show that the PLOT column exhibits good separation efficiency with resolution >3.0 and theoretical plate numbers over 6 × 104, as well as good intra-/inter-day repeatability and column-to-column repeatability. The column has been successfully applied for CEC analysis of three different types of samples without any further modification of the columns, including complicated peptide products from tryptic-digestion of proteins (lysozyme and BSA), ß-blockers (basic samples) and polycyclic aromatic hydrocarbons (neutral samples). Efficient separation has been achieved, which could be attributed to the enhanced surface-to-volume ratio of the PLOT column that will increase the interaction between solid phase and mobile phase in CEC. In addition, base-line separation of neutral samples indicates the reversed phase chromatographic property of the PLOT column, which could be induced by the residue of hexadecyltrimethylammonium bromide used in the fabrication process. Our study show that the present PLOT column is a promising approach that can significantly enhance CEC separation efficiency and could be of potential value in analysis of various different samples.

Rapid and sensitive tapered-capillary microextraction combined to on-line sample stacking-capillary electrophoresis for extraction and quantification of two beta-blockers in human urine.

A tapered-capillary microextraction (tCap-µEx) combining with field-amplified stacking (FASI) method for CE analysis was developed. The tCap-µEx method is based on the construction of a micro solid phase extraction (SPE) column by narrowing the end of a silica capillary from 530µm (inner diameter) to 20µm, enabling the packing of 45µm sorbent particles without a frit. Various parameters that may affect the microextraction and FASI-CE analysis have been investigated and optimized. This study shows that microextraction exhibits advantages of small sample and sorbent volumes (less than 200µL sample and 2µL sorbent) and fast extraction time of 6min. The method was successfully applied for efficient determination of atenolol and metoprolol in human urine samples, with recovery of 93.7-105.5% and RSD (n=3) lower than 8.5%. Twenty-one-fold and nineteen-fold average enhancement of detection sensitivity was achieved for atenolol and metoprolol, respectively, versus the CE method without tCap-µEx and FASI. The method is environmentally friendly and allows reuse of the sorbent at least 8 times without an obvious loss in performance. The results indicate that the proposed method could be potentially applied in a wide range of doping control, clinical, forensic toxicology, food analysis and environmental analyses.

Core-shell silica microsphere-based trypsin nanoreactor for low molecular-weight proteome analysis.

Core-shell mesoporous silica (CSMS) microspheres with tunable mesopores in the shell are highly desired in various bioapplications. With novel CSMS microspheres that are synthesized using a convenient two-phase process, we report in this study the analysis of low molecular-weight (MW < 30 kDa) proteins by combining size-exclusion separation and enzyme immobilization. The obtained CSMS microspheres possess uniform diameter (1.3 µm with a shell thickness of 57 nm), large and tunable perpendicular mesopores (7.9 nm), high surface area (55.5 m2/g), large pore volume (0.12 cm3/g) and excellent water dispersibility. The CSMS microsphere-based enzyme nanoreactors have been fabricated by immobilizing trypsin on the pore channels of the CSMS microspheres using either physical absorption or covalent binding via thiol or aldehyde group with a high loading capacity of 11.8-6.1 mg/g. Due to the unique fibrous pore structure, low MW proteins can enter the channels in the shell to interact with immobilized trypsin, followed by analysis of the digestion products using MALDI-TOF MS or electrophoresis (CE) techniques. The properties and analytical performance of different trypsin-immobilized CSMS microspheres has been systematically evaluated. The results show that the peptide-sequence coverage of the smaller protein is enhanced by using trypsin-CSMS microspheres, indicating the size-dependent digestion which results from the size-exclusion interaction of the mesopores against the high-MW proteins. The present study would pave the way for further applications of mesoporous materials in proteome analysis.

Screening Platform Based on Robolid Microplate for Immobilized Enzyme-Based Assays.

A facile, cost-effective, and high-throughput screening method was developed for enzyme-based assays based on Robolid/Microplate (RLMP) platform. The RLMP platform is constructed by immobilizing enzyme on commercial robolids and combining it with a standard 96-well microplate to achieve high-throughput analysis. The initiation and quenching of enzymatic reaction can be performed by simply sandwiching or unsealing the enzyme-immobilized robolids and the sample-containing microplate. This platform enables measurements of multiple target analytes simultaneously based on immobilized enzymatic reactions, with analysis time independent of the number of wells in the microplate. Using urea as the model analyte, we have shown that the RLMP platform exhibits large linear detection range of up to 10 mM, fast analysis time of 30 min/96 samples, as well as good reproducibility and stability. Measurements of urea in human urine and serum samples were performed using the RLMP platform and were compared with the commercial urea test kit. A good correlation was found between the two methods. This study shows that the present RLMP platform has promising prospects for detection of clinical markers and application in disease diagnosis and biochemical analysis.

Enzyme and inhibition assay of urease by continuous monitoring of the ammonium formation based on capillary electrophoresis.

We present here an easy-to-operate and efficient method for enzyme and inhibition assays of urease, which is a widely distributed and important enzyme that catalyzes the hydrolysis of urea to ammonia and CO2 . The assay was achieved by integrating CE technique and rapid on-line derivatization method, allowing us to continuously drive the sample to the capillary, thus to measure the amount of the product ammonia from the beginning to the end of the reaction. The method exhibits excellent repeatability with RSD as low as 2.5% for the initial reaction rate (n = 5), with the LOD of ammonia of 20 µM (S/N = 5). The enzyme activity as well as the inhibition of urease by Cu2+ were investigated using the present method. The results show that Cu2+ is a noncompetitive inhibitor on urease, in accordance with the result published in the literature. The enzyme activity and inhibition kinetic constants were obtained and were found to be consistent with the results of traditional off-line enzyme assays. Our study indicates that the present approach is a reliable and convenient method for analysis of the urease activity and inhibition kinetics by continuous on-line monitoring of the ammonium formation based on CE.

Highly effective Ir(x)Sn(1-x)O2 electrocatalysts for oxygen evolution reaction in the solid polymer electrolyte water electrolyser.

We developed an advanced surfactant-assistant method for the Ir(x)Sn(1-x)O(2) (0 < x ≤ 1) nanoparticle (NP) preparation, and examined the OER performances by a series of half-cell and full-cell tests. In contrast to the commercial Ir black, the collective data confirmed the outstanding activity and stability of the fabricated Ir(x)Sn(1-x)O(2) (x = 1, 0.67 and 0.52) NPs, which could be ascribed to the amorphous structure, good dispersion, high pore volume, solid-solution state and Ir-rich surface for bi-metal oxides, and relatively large size (10-11 nm), while Ir(0.31)Sn(0.69) exhibited poor electro-catalytic activity because of the separated two phases, a SnO(2)-rich phase and an IrO(2)-rich phase. Furthermore, compared with highly active IrO(2), the improved durability, precious-metal Ir utilization efficiency and correspondingly reduced Ir loading were realized by the addition of Sn component. When the Ir(0.52)Sn(0.48)O(2) cell operated at 80 °C using Nafion® 115 membrane and less than 0.8 mg cm(-2) of the noble-metal Ir loading, the cell voltages we achieved were 1.631 V at 1000 mA cm(-2), and 1.821 V at 2000 mA cm(-2). The IR-free voltage at the studied current density was very close to the onset voltage of oxygen evolution. The only 50 µV h(-1) of voltage increased for the 500 h durability test at 500 mA cm(-2). In fact, these results are exceptional compared to the performances for OER in SPEWE cells known so far. This work highlights the potential of using highly active and stable IrO(2)-SnO(2) amorphous NPs to enhance the electrolysis efficiency, reduce the noble-metal Ir loading and thus the cost of hydrogen production from the solid polymer electrolyte water electrolysis.