John Rick

Direct In situ Observation of Li2O Evolution on Li-Rich High-Capacity Cathode Material, Li[NixLi(1–2x)/3Mn(2–x)/3]O2 (0 ≤ x ≤0.5)

High-capacity layered, lithium-rich oxide cathodes show great promise for use as positive electrode materials for rechargeable lithium ion batteries. Understanding the effects of oxygen activating reactions on the cathodes surface during electrochemical cycling can lead to improvements in stability and performance. We used in situ surfaced-enhanced Raman spectroscopy (SERS) to observe the oxygen-related surface reactions that occur during electrochemical cycling on lithium-rich cathodes. Here, we demonstrate the direct observation of Li2O formation during the extended plateau and discuss the consequences of its formation on the cathode and anode. The formation of Li2O on the cathode leads to the formation of species related to the generation of H2O together with LiOH and to changes within the electrolyte, which eventually result in diminished performance. Protection from, or mitigation of, such devastating surface reactions on both electrodes will be necessary to help realize the potential of high-capacity cathode materials (270 mAhg(-1) versus 140 mAhg(-1) for LiCoO2) for practical applications.

Bimetallic PtM (M = Pd, Ir) nanoparticle decorated multi-walled carbon nanotube enzyme-free, mediator-less amperometric sensor for H2O2

A new highly catalytic and intensely sensitive amperometric sensor based on PtM (where M=Pd, Ir) bimetallic nanoparticles (NPs) for the rapid and accurate estimation of hydrogen peroxide (H(2)O(2)) by electrooxidation in physiological conditions is reported. PtPd and PtIr NPs-decorated multiwalled carbon nanotube nanocatalysts (PtM/MWCNTs) were prepared by a modified Watanabe method, and were characterized by XRD, TEM, ICP, and XAS. The sensors were constructed by immobilizing PtM/MWCNTs nanocatalysts in a Nafion film on a glassy carbon electrode. Both PtPd/MWCNTs and PtIr/MWCNTs assemblies catalyzed the electrochemical oxidation of H(2)O(2). Cyclic voltammetry characterization measurements revealed that both the PtM (M=Pd, Ir)/MWCNTs/GCE possessed similar electrochemical surface areas (∼0.55 cm(2)), and electron transfer rate constants (∼1.23 × 10(-3)cms(-1)); however, the PtPd sensor showed a better performance in H(2)O(2) sensing than did the PtIr counterpart. Explanations were sought from XAS measurements to explain the reasons for differences in sensor activity. When applied to the electrochemical detection of H(2)O(2), the PtPd/MWCNTs/GC electrode exhibited a low detection limit of 1.2 μM with a wide linear range of 2.5-125 μM (R(2)=0.9996). A low working potential (0V (SCE)), fast amperometric response (<5s), and high sensitivity (414.8 μA mM(-1)cm(-2)) were achieved at the PtPd/MWCNTs/GC electrode. In addition, the PtPd/MWCNTs nanocatalyst sensor electrode also exhibited excellent reproducibility and stability. Along with these attractive features, the sensor electrode also displayed very high specificity to H(2)O(2) with complete elimination of interference from UA, AA, AAP and glucose.

Using hematite for photoelectrochemical water splitting: a review of current progress and challenges

Photoelectrochemical (PEC) water splitting is a promising technology for solar hydrogen production to build a sustainable, renewable and clean energy economy. Hematite (α-Fe2O3) based photoanodes offer promise for such applications, due to their high chemical stability, great abundance and low cost. Despite these promising properties, progress towards the manufacture of practical water splitting devices has been limited. This review is intended to highlight recent advancements and the limitations that still hamper the full utilization of hematite electrodes in PEC water splitting systems. We review recent progress in manipulating hematite for PEC water splitting through various approaches, focused on e.g. enhancing light absorption, water oxidation kinetics, and charge carrier collection efficiency. As the morphology affects various properties, progress in morphological characterization from thicker planar films to recent ultrathin nanophotonic morphologies is also examined. Special emphasis has been given to various ultrathin films and nanophotonic structures which have not been given much attention in previous review articles.

Fabrication and application of amperometric glucose biosensor based on a novel PtPd bimetallic nanoparticle decorated multi-walled carbon nanotube catalyst

A sensitive, selective and stable amperometric glucose biosensor employing novel PtPd bimetallic nanoparticles decorated on multi-walled carbon nanotubes (PtPd-MWCNTs) was investigated. PtPd-MWCNTs were prepared by a modified Watanabe method, and characterized by XRD and TEM. The biosensor was constructed by immobilizing the PtPd-MWCNTs catalysts in a Nafion film on a glassy carbon electrode. An inner Nafion film coating was used to eliminate common interferents such as uric acid, ascorbic acid and fructose. Finally, a highly porous surface with an orderly three-dimensional network enzyme layer (CS-GA-GOx) was fabricated by electrodeposition. The resulting biosensor exhibited a good response to glucose with a wide linear range (0.062-14.07 mM) and a low detection limit 0.031 mM. The biosensor also showed a short response time (within 5 s), and a high sensitivity (112 μA mM(-1)cm(-2)). The Michaelis-Menten constant (K(m)) was determined as 3.3 mM. In addition, the biosensor exhibited high reproducibility, good storage stability and satisfactory anti-interference ability. The applicability of the biosensor to actual serum sample analysis was also evaluated.

Heterostructured Cu2O/CuO decorated with nickel as a highly efficient photocathode for photoelectrochemical water reduction

Here we report the design, synthesis and characterization of a novel Cu2O/CuO heterojunction decorated with a nickel cocatalyst as a highly efficient photocathode for solar hydrogen production. The heterojunction structure was shown and examined by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Tip-enhanced Raman spectroscopy (TERS). Due to the synergistic effect, the Cu2O/CuO heterojunction gave a remarkably improved photocurrent density (−2.1 mA cm−2), i.e. 3.1 times higher than a Cu2O photoelectrode. Additionally, the Cu2O/CuO heterojunction, when decorated with the nickel cocatalyst, showed six-fold and two-fold increases in photocurrent density (−4.3 mA cm−2) respectively when compared to Cu2O and the bare Cu2O/CuO at 0 V vs. RHE under AM 1.5 illumination (100 mW cm−2). Interestingly, the Ni decorated Cu2O/CuO photocathode showed an impressive solar conversion efficiency of 2.71% at −0.4 V vs. Pt, i.e. 467% higher compared to the bare Cu2O/CuO. After 20 minutes of standard solar illumination, 87.7% of the initial photocurrent density was retained for the nickel decorated Cu2O/CuO heterojunction. This is more than 1.5 times that of the bare Cu2O/CuO (53.6%), suggesting that surface modification with Ni not only effectively promotes water splitting but also stabilizes the photoelectrode. The enhanced photoelectrochemical performance is attributable to the efficient charge transfer and protective role of Ni, the improved crystallinity and the synergistic effect of the heterojunction in light absorption and charge separation. This inexpensive photocathode with increased photocurrent density and photostability offers a higher promise for solar hydrogen production.

Ultrathin TiO2-coated MWCNTs with excellent conductivity and SMSI nature as Pt catalyst support for oxygen reduction reaction in PEMFCs

The sluggish kinetics of the oxygen reduction reaction (ORR), the instability of platinum on the carbon support, and carbon corrosion are still critical issues affecting the activity and long-term durability of polymer electrolyte membrane fuel cells. An ideal solution would be to modify the catalytic supports to enhance the durability and performance of supported catalysts. Here we have synthesized multiwalled carbon nanotube (MWCNT) supported ultrathin TiO2 films (MWCNT@UT-TiO2) using a simple modified sol–gel method. Our approach takes advantage of the strong metal support interactions (SMSIs) between the MWCNT@UT-TiO2 support and platinum nanoparticles, which results in a decrease of the d-band vacancy of platinum due to electron transfer from the support, thereby enhancing the performance of the supported catalysts. Our results revealed that Pt–MWCNT@UT-TiO2 has better catalytic activity and durability compared to Pt–MWCNT and Pt–C with equivalent Pt loadings.

Robust non-carbon Ti0.7Ru0.3O2 support with co-catalytic functionality for Pt: enhances catalytic activity and durability for fuel cells

Multifunctional binary metal oxide (Ti0.7Ru0.3O2), a novel functionalised co-catalytic support for Pt, is synthesized in a simple one-step hydrothermal process at low temperature. In practical applications Ti0.7Ru0.3O2 offers both excellent improvements in electrocatalytic activity and durability over commercial carbon supported Pt and PtRu catalysts for direct methanol fuel cell (DMFC), while at the molecular level it provides advantages in terms of its high surface area, and the strong interactions between Pt and the co-catalytic support. The Ti0.7Ru0.3O2 support acts as a co-catalyst supporting Pt activity, due to the high proton conductivity of hydrated Ti0.7Ru0.3O2 which underlies a ‘bifunctional mechanism’ and the synergistic effect between Pt and Ti0.7Ru0.3O2, modifying the electronic nature of the metal particles as well, which additionally enhances CO-tolerance, the catalytic activity and durability for methanol and hydrogen oxidation. Additionally, Ti0.7Ru0.3O2 can be fabricated as a much thinner catalyst layer resulting in improving mass transport kinetics, giving a broad scope for its wider application in other fuel cells, as demonstrated here by its application in a direct methanol fuel cell (DMFC) and polymer electrolyte membrane fuel cell (PEMFC) and can also be extended to other areas such as catalytic biosensor technology.

A new graphene-modified protic ionic liquid-based composite membrane for solid polymer electrolytes

The production of a solid polymer electrolyte with high ionic conductivity and mechanical properties is the main fabrication challenge in application of polymer electrolyte membranes. This paper describes a novel polymer electrolyte membrane using protic ionic liquids (PILs) with ionic liquid polymer modified graphene (G) sheets [denoted PIL(NTFSI)-G] that exhibit dramatic enhancements in ionic conductivity (257.4%) and mechanical properties (345% improvement in tensile strength and a near 25-fold increase in modulus were achieved at 150 °C) with a minimal loading of PIL(NTFSI)-G (0.5 wt%). The addition of graphene, by sparing the high-cost PIL addition, gives a 20% cost-saving. The homogeneous distribution of graphene sheets as a 3D network through the polymer matrix in the composite membrane provides a high degree of continuous and interconnected transfer channels to facilitate ion transfer and enhance nanofiller–matrix adhesion to reinforce mechanical properties. This newly developed material provides a potential route toward the design and fabrication of polymer electrolytes.

Kinetically Controlled Autocatalytic Chemical Process for Bulk Production of Bimetallic Core–Shell Structured Nanoparticles

Although bimetallic core@shell structured nanoparticles (NPs) are achieving prominence due to their multifunctionalities and exceptional catalytic, magnetic, thermal, and optical properties, the rationale underlying their design remains unclear. Here we report a kinetically controlled autocatalytic chemical process, adaptable for use as a general protocol for the fabrication of bimetallic core@shell structured NPs, in which a sacrificial Cu ultrathin layer is autocatalytically deposited on a dimensionally stable noble-metal core under kinetically controlled conditions, which is then displaced to form an active ultrathin metal-layered shell by redox-transmetalation. Unlike thermodynamically controlled under-potential deposition processes, this general strategy allows for the scaling-up of production of high-quality core-shell structured NPs, without the need for any additional reducing agents and/or electrochemical treatments, some examples being Pd@Pt, Pt@Pd, Ir@Pt, and Ir@Pd. Having immediate and obvious commercial potential, Pd@Pt NPs have been systematically characterized by in situ X-ray absorption, electrochemical-FTIR, transmission electron microscopy, and electrochemical techniques, both during synthesis and subsequently during testing in one particularly important catalytic reaction, namely, the oxygen reduction reaction, which is pivotal in fuel cell operation. It was found that the bimetallic Pd@Pt NPs exhibited a significantly enhanced electrocatalytic activity, with respect to this reaction, in comparison with their monometallic counterparts.

Self-focusing Au@SiO2 nanorods with rhodamine 6G as highly sensitive SERS substrate for carcinoembryonic antigen detection

A highly sensitive self-focusing surface-enhanced Raman scattering (SERS) methodology has been developed using Au@SiO2 core-shell nanorods for carcinoembryonic antigen (CEA) detection. The SERS enhancement factor was evaluated for anisotropic Au@SiO2 nanorods with silica shells of various thicknesses, upon which Rhodamine 6G (R6G) dye was applied as a reporter molecule for the quantitative determination of CEA. The highest R6G signal was attained with a silica layer of 1-2 nm thickness. The self-focusing character originates from the antibody-antigen interaction, which facilitates the SERS probes assembly and significantly increases the detection sensitivity of the CEA. Our results show that the SERS technique is able to detect CEA within a wide concentration range. With an extremely low limit of detection (LOD) of 0.86 fg mL-1, the Au@SiO2 nanoprobes potentially enable the early diagnosis of cancer. Our work offers a low-cost route to the fabrication of sensing devices able to be used for monitoring cancer progression in natural matrices, such as blood.