Rou Jun Toh

Transition metal (Mn, Fe, Co, Ni)-doped graphene hybrids for electrocatalysis.

The development of electrocatalysts is crucial for renewable energy applications. Metal-doped graphene hybrid materials have been explored for this purpose, however, with much focus on noble metals, which are limited by their low availability and high costs. Transition metals may serve as promising alternatives. Here, transition metal-doped graphene hybrids were synthesized by a simple and scalable method. Metal-doped graphite oxide precursors were thermally exfoliated in either hydrogen or nitrogen atmosphere; by changing exfoliation atmospheres from inert to reductive, we produced materials with different degrees of oxidation. Effects of the presence of metal nanoparticles and exfoliation atmosphere on the morphology and electrocatalytic activity of the hybrid materials were investigated using electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Doping of graphene with transition metal nanoparticles of the 4th period significantly influenced the electrocatalysis of compounds important in energy production and storage applications, with hybrid materials exfoliated in nitrogen atmosphere displaying superior performance over those exfoliated in hydrogen atmosphere. Moreover, nickel-doped graphene hybrids displayed outstanding electrocatalytic activities towards reduction of O2 when compared to bare graphenes. These findings may be exploited in the research field of renewable energy.

Bioavailability of Metallic Impurities in Carbon Nanotubes Is Greatly Enhanced by Ultrasonication

Metallic impurities within carbon nanotubes (CNTs) are considered as the main cause of their toxicity. Ultrasonication is a common procedure used to purify and obtain homogeneous dispersions of CNTs as well as to mix them with other components for further processing into composites. Herein, the influence of ultrasonication upon the bioavailability of metallic impurities in CNTs was investigated. We showed that even ultrasonication times as short as 5 min significantly enhanced the bioavailability of metallic impurities, which can therefore interact more actively with biologically important molecules. These findings will have profound impact on the processing of CNTs as well as on nanotoxicity studies.

Transition Metal Oxides for the Oxygen Reduction Reaction: Influence of the Oxidation States of the Metal and its Position on the Periodic Table.

Electrocatalysts have been developed to meet the needs and requirements of renewable energy applications. Metal oxides have been well explored and are promising for this purpose, however, many reports focus on only one or a few metal oxides at once. Herein, thirty metal oxides, which were either commercially available or synthesized by a simple and scalable method, were screened for comparison with regards to their electrocatalytic activity towards the oxygen reduction reaction (ORR). We show that although manganese, iron, cobalt, and nickel oxides generally displayed the ability to enhance the kinetics of oxygen reduction under alkaline conditions compared with bare glassy carbon, there is no significant correlation between the position of a metal on the periodic table and the electrocatalytic performance of its respective metal oxides. Moreover, it was also observed that mixed valent (+2, +3) oxides performed the poorest, compared with their respective pure metal oxides. These findings may be of paramount importance in the field of renewable energy.

Catalytic properties of group 4 transition metal dichalcogenides (MX2; M = Ti, Zr, Hf; X = S, Se, Te)

Interest in layered transition metal dichalcogenides (TMDs) has proliferated due to their properties, making them promising materials for electrochemical applications. Despite this, almost exclusive attention has been placed on group 6 TMDs. Hitherto, there has been a lack of understanding of the electrochemical behaviour of group 4 TMDs, which could serve as promising materials for electrochemical applications with their semiconducting properties. In this work, we provide a first insight into the inherent electrochemistry of group 4 TMDs (i.e., TiS2, TiSe2, TiTe2, ZrS2, ZrSe2, ZrTe2, HfS2, HfSe2 and HfTe2) and their catalytic activities towards the hydrogen evolution reaction (HER). In particular, HfS2 is electrochemically inert within a wide potential range of −1.8 V to +1.8 V vs. Ag/AgCl and displays superior HER activity compared to the other group 4 TMDs, making it a promising candidate for electrochemical sensing applications. Towards the aim of tuning their HER catalytic properties, the materials are subjected to electrochemical treatment. Electrochemical activation towards the HER is displayed for ZrSe2 and HfSe2via both electrochemical oxidation and reduction, and TiTe2via electrochemical reduction. X-ray photoelectron spectroscopy (XPS) analysis points towards the importance of material purity in tuning the catalytic performances of group 4 TMDs. Such findings provide a foundational understanding of the electrochemistry of group 4 TMDs, which when applied appropriately can springboard this field of research towards achieving aims in electrochemical applications.

Direct In Vivo Electrochemical Detection of Haemoglobin in Red Blood Cells

The electrochemical behavior of iron ion in haemoglobin provides insight to the chemical activity in the red blood cell which is important in the field of hematology. Herein, the detection of haemoglobin in human red blood cells on glassy carbon electrode (GC) was demonstrated. Red blood cells or raw blood cells was immobilized on a glassy carbon electrode surface with Nafion films employed to sandwich the layer of biological sample firmly on the electrode surface. Cyclic voltammetry (CV) analyses revealed a well-defined reduction peak for haemoglobin at about −0.30 V (vs. Ag/AgCl) at the red blood cell (GC-Nf-RBC-3Nf) and blood (GC-Nf-B-3Nf) film modified GCE in a pH 3.5 phosphate buffer solution. We further demonstrated that the complex biological conditions of a human red blood cell displayed no interference with the detection of haemoglobin. Such findings shall have an implication on the possibilities of studying the electrochemical behaviour of haemoglobin directly from human blood, for various scientific and clinical purposes.

MoSe2 Nanolabels for Electrochemical Immunoassays

There is huge interest in biosensors as a result of the demand for personalized medicine. In biomolecular detection, transition-metal dichalcogenides (TMDs) can be used as signal-enhancing elements. Herein, we utilize a solution-based electrochemical exfoliation technique with bipolar electrodes to manufacture MoSe2 nanolabels for biomolecular detection. Prepared MoSe2 nanoparticles (NPs) exhibit electrocatalytic activity toward the hydrogen evolution reaction (HER), and such a property allows it to act as a robust label for magneto-immunoassays toward protein detection. The magneto-immunoassay also displayed good selectivity, a wide linear range of 2 to 500 ng mL-1, high sensitivity (LOD = 1.23 ng mL-1) and reproducibility (RSD = 9.7%). These findings establish the viability and reproducibility of such an exfoliation technique for TMD nanolabels for the development of low costs and efficient biosensing systems.

Iridium- and Osmium-decorated Reduced Graphenes as Promising Catalysts for Hydrogen Evolution

Renewable energy sources are highly sought after as a result of numerous worldwide problems concerning the environment and the shortage of energy. Currently, the focus in the field is on the development of catalysts that are able to provide water splitting catalysis and energy storage for the hydrogen evolution reaction (HER). While platinum is an excellent material for HER catalysis, it is costly and rare. In this work, we investigated the electrocatalytic abilities of various graphene-metal hybrids to replace platinum for the HER. The graphene materials were doped with 4f metals, namely, iridium, osmium, platinum and rhenium, as well as 3d metals, namely, cobalt, iron and manganese. We discovered that a few hybrids, in particular iridium- and osmium-doped graphenes, have the potential to become competent electrocatalysts owing to their low costs and-more importantly-to their promising electrochemical performances towards the HER. One of the more noteworthy observations of this work is the superiority of these two hybrids over MoS2 , a well-known electrocatalyst for the HER.

Haemoglobin electrochemical detection on various reduced graphene surfaces: well-defined glassy carbon electrode outperforms the graphenoids

Monitoring the direct electron transfer reactions of haemoglobin is important for understanding of chemical changes within the red blood cell for haematological studies. However, the facilitation of electron transfer between haemoglobin and bare solid electrodes is challenging. Herein, the influence of carbon nanomaterials; graphite oxide (GO), chemically reduced graphene oxide (CRGO), graphene oxide (GO′), electrochemically reduced graphene oxide (ERGO) and edge plane pyrolytic graphite (EPPG); on the electron transfer between haemoglobin in solution and solid electrodes was investigated. We showed that GO, CRGO, GO′ and ERGO did not exhibit improvement to the electron transfer characteristics of haemoglobin in solution, and bare glassy carbon remains an appropriate electrode material for such application in electrochemical sensing. These findings are in contrast to previous studies, which report an enhancement in direct electron transfer characteristics of haemoglobin immobilized on the electrode surface with employment of carbon nanomaterials, and will have profound impact on further investigation of the electron transfer characteristics of hemoglobin.

Group 6 Layered Transition-Metal Dichalcogenides in Lab-on-a-Chip Devices: 1T-Phase WS2 for Microfluidics Non-Enzymatic Detection of Hydrogen Peroxide

Two-dimensional (2D) layered transition-metal dichalcogenides (TMDs) have been placed in the spotlight for their advantageous properties for catalytic and sensing applications. However, little work is done to explore and exploit them in enhancing the performance of analytical lab-on-a-chip (LOC) devices. In this work, we demonstrate a simple, sensitive, and low-cost fabrication of electrochemical LOC microfluidic devices to be used for enzymatic detection. We integrated four t-BuLi exfoliated, group 6 TMD materials (MoS2, MoSe2, WS2, and WSe2) within the LOC devices by the drop-casting method and compared their performance for H2O2 detection. The 1T-phase WS2-based LOC device outperformed the rest of the TMD materials and exhibited a wide range of linear response (20 nM to 20 μM and 100 μM to 2 mM), low detection limit (2.0 nM), and good selectivity for applications in real sample analysis. This work may facilitate the expanded use of electrochemical LOC microfluidics, with its easier integrability, for applications in the field of biodiagnostics and sensing.

Ultrapure Molybdenum Disulfide Shows Enhanced Catalysis for Hydrogen Evolution over Impurities‐Doped Counterpart

The development of electrocatalysts to meet the requirements of renewable energy applications has seen much attention placed on transition‐metal dichalcogenide (TMD) materials owing to their promising properties. In particular, the strategy of atomic doping has garnered some success in tuning the electronic properties and harnessing the vast potential that TMDs can offer in the catalysis of the hydrogen evolution reaction (HER). Moreover, with computational studies reporting the promising effects of transition‐metal doping, such a strategy has been adopted with much enthusiasm. Herein, we consider one of the most prevalent TMDs, that is, MoS2, and the possible presence of impurities arising from its preparation method and starting materials that may act as dopants to affect its electronic and catalytic properties. An ultrapure MoS2 material was synthesized and compared with a relatively impure MoS2 sample obtained commercially. Ultrapure MoS2 was found to outperform its impurities‐doped counterpart in HER catalysis. These findings not only provide valuable insight into the influence of parts‐per‐million concentrations of impurities on the catalytic activity of TMD materials but also highlight the importance of the intentional and proper design of atomic doping to realize its true effects. At the same time, the need for a more in‐depth understanding and evaluation of the benefits of the atomic‐doping strategy in the experimental setting as a means to harness the potential of TMDs as catalysts for hydrogen evolution is also revealed.