Chee Shan Lim

Layered transition metal oxyhydroxides as tri-functional electrocatalysts

Layered transition metal-based materials have been intensively explored for their electrocatalytic capabilities in energy-related applications such as the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) lately. These reactions are kinetically sluggish, and require catalysts to promote their efficiency. Since their discovery and characterization decades ago, the catalytic properties of metal oxyhydroxides have not been profoundly studied. It was only in recent years when emphasis was placed on them again, mainly as possible OER catalysts. In this work, we wish to delve deeper into several layered first-row transition metal (cobalt, chromium, iron, manganese and nickel) oxyhydroxides, and investigate their inherent electrochemistry and electrocatalytic behaviors for HER and OER, as well as the oxygen reduction reaction (ORR). Characterisation of these materials was performed using scanning electron microscopy, X-ray powder diffraction, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy prior to electrochemical studies. Among the five layered oxyhydroxides examined, cobalt and nickel oxyhydroxides exhibited better electrocatalytic properties than the other three layered oxyhydroxides mainly in HER and OER.

Detection of biomarkers with graphene nanoplatelets and nanoribbons

Well-defined graphene nanosheets have become increasingly popular in the electrochemical detection and quantification of small molecules. In this work, the electrochemical oxidation of biomarkers such as uric acid, ascorbic acid, dopamine, NADH and DNA bases, namely guanine and adenine, was performed using cyclic voltammetry and differential pulse voltammetry to compare the electrochemical properties of electrochemically reduced nanoplatelets (ENPs) and electrochemically reduced nanoribbons (ENRs). The graphene materials displayed better electrochemical performances than the bare glassy carbon surface. Between the two graphene materials, the oxidation of biomarkers occurred at lower oxidation potentials on the ENP surface. The sensitivities of the two graphene surfaces varied when different biomarkers were studied. The ENP surface showed enhanced sensitivities for ascorbic acid, while the ENR surface exhibited higher sensitivities for uric acid and dopamine. As for the DNA bases analysed, both guanine and adenine were oxidised at lower potentials on the ENP surface than the ENR surface. The ENP surface displayed a better sensitivity for guanine, whereas the oxidation of adenine was more sensitive on the ENR surface.

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.

High temperature superconducting materials as bi-functional catalysts for hydrogen evolution and oxygen reduction

As the world progresses towards green and cost-effective energy applications, it is imperative to discover and introduce viable electrocatalysts to replace platinum, which is expensive and scarce. High-temperature superconductors have been intensively studied at the end of the 20th century owing to their unique electrical behaviour; nonetheless, we wish to show their interesting electrocatalytic properties as well. This work seeks to investigate the feasibility of two high-temperature superconductors, YBa2Cu3O7 (YBCO) and Bi2Sr2CaCu2O8 (BSCCO) in catalysing the hydrogen evolution and oxygen reduction reactions electrochemically. These materials can be easily synthesized by solid state reactions and this in combination with the fairly impressive electrocatalytic properties displayed in our study, mean that they definitely possess the potential to replace platinum as prospective electrocatalysts.

Electrochemistry of Layered Graphitic Carbon Nitride Synthesised from Various Precursors: Searching for Catalytic Effects

Graphitic carbon nitride (g-C3 N4 ), synthesised by pyrolysis of different precursors (dicyandiamide, melamine and urea) under varying reaction conditions (air and nitrogen gas) is subjected to electrochemical studies for the elucidation of the inherent catalytic efficiency of the pristine material. Contrary to popular belief, pristine g-C3 N4 shows negligible, if any, enhancement in its electrochemical behaviour in this comprehensive study. Voltammetric analysis reveals g-C3 N4 to display similar catalytic efficiency to the unmodified glassy carbon electrode surface on which the bulk material was deposited. This highlights the non-catalytic nature of the pristine material and challenges the feasibility of using g-C3 N4 as a heterogeneous catalyst to deliver numerous promised applications.

Inherent Electrochemistry of Layered Post‐Transition Metal Halides: The Unexpected Effect of Potential Cycling of PbI2

The development of two-dimensional nanomaterials has expedited the growth of advanced technological applications. PbI2 is a layered inorganic solid with important and unique properties suitable for applications in the detection of electromagnetic radiation. While the optical and electrical properties of layered PbI2 have been generally established, its electrochemistry has remained largely unexplored. In this work, we examine the inherent electrochemistry of PbI2 in relation to its morphological and structural properties. A direct comparison between commercially available and solution-grown PbI2 showed high similarity in properties based on characterizations by X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The respective layered PbI2 materials also exhibited similar inherent electrochemistry. Electrochemical potential cycling of PbI2 in phosphate buffer resulted in the dissolution of iodide ions from PbI2 to form complex lead-phosphate-chloride with the oxygen groups of the phosphate ions while retaining the hexagonal structure. In the case of KCl solution, the formation of PbO2 was observed.

Electrochemical properties of layered SnO and PbO for energy applications

In this paper we synthetized four different lead oxides with tetragonal or orthorhombic symmetry either by thermal decomposition or a chemical route. Another two tin oxides were also synthesized by thermal decomposition and chemical route respectively. We analysed their structure by XRD and SEM and chemical composition by EDS and XPS. Thermal decomposition was analysed using STA. The surface areas were determined by BET. Electrochemical behavior such as heterogeneous electron transfer rate, electrocatalytic properties in hydrogen evolution and oxygen reduction reactions were also investigated by cyclic voltammetry and linear sweep voltammetry. Results suggest that studied materials are promising candidates for catalysis or various applications in energy management.