Rational design of non-precious metal based catalysts for highly efficient electrochemical oxygen evolution

Electrolytic water splitting has the capability to store the electricity generated from renewable energy resources in the form of hydrogen (H2) fuel. Development of efficient, inexpensive electrolytic water splitting system, combining with hydrogen fuel cells, will provide continuous usage of intermittent renewable energies with minimum environmental impacts. The major hurdle impedes the large-scale applications of the electrolytic water splitting system is the sluggish oxygen evolution reaction (OER) at anode, which requires noble metal oxide based catalysts to lower the overpotential and generate hydrogen at an appreciable current density. However, these noble metals are costly and their supply is not sustainable. As a result, the development of efficient, non-precious metal-based OER catalyst materials is highly demanded. This thesis focuses on design, synthesis and characterisation of nanoscale transition metal based catalysts as a new class of cost effective electrocatalysts for highly efficient oxygen evolution. To this end, a range of novel nanostructured OER catalysts are synthesised including (1) mesoporous cobalt oxide catalysts embedded with gold nanoparticles (Au/mCo3O4), (2) a micro/nanostructured hierarchical 3D nickel-iron hydroxides electrode, (3) a multifunctional amorphous nickel-iron-colbalt hydroxides decorated 3D electrode, (4) nanocrystalline cobalt oxides anchored onto mildly oxidised multiwall carbon nanotubes, and (5) transparent Co3O4 nanoparticles/graphene electrode achieved by layer-by-layer assembly. New synthesis techniques are developed to synthesise these catalysts, and their catalytic properties are investigated with electrochemical techniques (cyclic voltammetry, rotating disc electrode voltammetry, chronoamperometry, chronopotentiometry). The atomic, electronic and surface structures of these catalysts are investigated with a variety of physical characterisations (X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy), and correlated with their catalytic properties. The intrinsic catalytic activity and structure-property relationships of these catalysts are also established. Importantly, the results suggest that, via rational design, transition metal based catalysts that exhibit comparable, or even superior OER catalytic activity to benchmark RuO2 and IrO2 catalysts can be achieved with significantly reduced fabrication cost

Metal-free carbon-based catalysts design for oxygen reduction reaction towards hydrogen peroxide: From 3D to 0D

Hydrogen peroxide (H2O2) is a versatile and environmentally-friendly oxidant with widespread industrial applications. In recent years, electrochemical production of H2O2 through the two-electron oxygen reduction reaction (ORR) pathway has been considered a promising alternative to the energy-intensive anthraquinone process. Among various electrocatalysts proposed for electrochemical generation of H2O2, metal-free carbon-based materials have attracted significant attention due to their low cost and large abundance. In this review, recent progress made in different types of metal-free carbon-based catalysts is presented. The fundamental aspects of the ORR mechanism and methodologies of ORR performance evaluation are introduced. Different metal-free electrocatalysts are then reviewed based on their dimensions, including three-dimensional, two-dimensional, one-dimensional, and zero-dimensional (3D, 2D, 1D, and 0D, respectively) catalysts. Various strategies, such as heteroatom doping, structural engineering, and defect engineering are examined for their role in enhancing catalytic efficiency. Furthermore, surface and interfacial engineering for achieving high H2O2 production is discussed. Lastly, challenges and opportunities in this field are proposed to guide future research toward the rational design of metal-free catalysts for the electrochemical production of H2O2.</p

Electrochemistry of Room Temperature Protic Ionic Liquids: A Critical Assessment for Use as Electrolytes in Electrochemical Applications

Ten room temperature protic ionic liquids (RTPILs) have been prepared from low-molecular-weight Brønsted acids and amines with high purity and minimal water content, and their electrochemical characteristics determined using cyclic, microelectrode, and rotating disk electrode voltammetries. Potential windows of the 10 RTPILs were established at glassy carbon, gold, and platinum electrodes, where the largest potential window is generally observed with glassy carbon electrodes. The two IUPAC recommended internal potential reference systems, ferrocene/ferrocenium and cobaltocenium/cobaltocene, were determined for the 10 RTPILs, and their merits as well as limitations are discussed. Other electrochemical properties such as mass transport and double layer capacitances were also investigated. The potential applications of these RTPILs as electrolytes for electrochemical energy devices were discussed, and two novel applications using PILs for metal deposition and water electrolysis were demonstrated

Cadmium sulfide Co-catalyst reveals the crystallinity impact of nickel oxide photocathode in photoelectrochemical water splitting

Nickel oxide (NiO) with p-type semiconducting behaviour was prepared via a direct anodisation of nickel (Ni) foam followed by calcination treatment. This method offers a direct photoelectrode synthesis without the intermediate step using a pre-synthesised NiO powder. NiO photocathodes with modulated crystallinity were prepared under elevated calcination temperatures. The beneficial effect of having higher crystallinity in generating higher cathodic photocurrent became obvious in the aid of cadmium sulfide (CdS) deposition. It was found that CdS can promote the excited charge transportation of NiO towards water reduction, thus revealing the effect of NiO crystallinity modulation. The role of CdS as co-catalyst rather than a photosensitiser can be useful in the future design of photoelectrodes

Oxygen Reduction Reaction in Room Temperature Protic Ionic Liquids

The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbon electrodes using cyclic voltammetry and potential-step chronoamperometry in 11 room temperature protic ionic liquids (PILs). The diffusion coefficient and solubility of oxygen in seven PILs were determined by nonlinear curve fitting of potential-step chronoamperometry at a platinum microelectrode. The diffusion coefficient of oxygen in the PILs was consistently on the order of 10^–6 cm² s^–1. The ORR in the PILs was found to largely follow an electrochemical–chemical–electrochemical–chemical (ECEC) mechanism, as demonstrated by digital simulation of cyclic voltammograms at platinum, gold, and glassy carbon electrodes. The influence of electrode material on peak potential, heterogeneous rate constant, and transfer coefficient was studied. The influence of temperature on kinetics and thermodynamic properties like activation energy of ORR, activation energy of diffusion, and enthalpy of dissolution of oxygen in ethylammonium nitrate, bis­(methoxyethyl)­ammonium benzoate, and bis-(methoxyethyl)­ammonium sulfamate was also investigated

Antipoisoning Nickel-Carbon Electrocatalyst for Practical Electrochemical CO2 Reduction to CO

The feasibility of utilizing electrochemical reduction of CO2 (CO2RR) to close the global carbon cycle is hindered by the absence of practical electrocatalysts that can be adopted in large CO2 emitting sources with impurities. To address this, we use density functional theory (DFT) calculations to design a strategy to develop Ni coordinated graphitic carbon shells (referred as Ni@NC-900) catalyst. This strategy not only prolongs stability and endows antipoisoning properties of the catalyst but also reforms the electronic structure of the outer graphitic carbon shell to make it active for CO2RR. As a result, Ni@ NC-900 demonstrates a high conversion of CO2 to CO with a Faradaic efficiency (FECO) of 96% and a partial current density for CO (jCO) of ∼−17 mA cm−2 at an applied potential of −1 V versus reversible hydrogen electrode (RHE). This activity can be further scaled up to attain a jCO of ∼30 mA cm−2 for 18 h at a cell voltage of 2.6 V in a high-throughput continuous gas diffusion electrode (GDE) system. In addition to exhibiting high activity and stability, Ni@NC-900 displays exceptional tolerance toward impurities (from SOx, NOx, CN−), highlighting the suitability of these rationally designed catalysts for large-scale application in fossil-fuel based power plantsThe work was supported by the Australian Research Council (ARC) under the Laurate Fellowship Scheme FL-140100081, Discovery Early Career Researcher Award DE170100375 and funding from the UNSW Digital Grid Futures Institute, UNSW Sydney under a crossdisciplinary fund scheme

Stabilizing the Unstable: Chromium Coating on NiMo Electrode for Enhanced Stability in Intermittent Water Electrolysis

Hydrogen production through water electrolysis is a promising method to utilize renewable energy in the context of urgent need to phase out fossil fuels. Nickel-molybdenum (NiMo) electrodes are among the best performing non-noble metal-based electrodes for hydrogen evolution reaction in alkaline media (alkaline HER). Albeit exhibiting stable performance in electrolysis at a constant power supply (i.e., constant electrolysis), NiMo electrodes suffer from performance degradation in electrolysis at an intermittent power supply (i.e., intermittent electrolysis), which is emblematic of electrolysis powered directly by renewable energy (such as wind and solar power sources). Here we reveal that NiMo electrodes were oxidized by dissolved oxygen during power interruption, leading to vanishing of metallic Ni active sites and loss of conductivity in MoOxsubstrate. Based on the understanding of the degradation mechanism, chromium (Cr) coating was successfully applied as a protective layer to inhibit oxygen reduction reaction (ORR) and significantly enhance the stability of NiMo electrodes in intermittent electrolysis. Further, combining experimental and Molecular Dynamics (MD) simulations, we demonstrate that the Cr coating served as a physical barrier inhibiting diffusion of oxygen, while still allowing other species to pass through. Our work offers insights into electrode behavior in intermittent electrolysis, as well as provides Cr coating as a valid method and corresponding deep understanding of the factors for stability enhancement, paving the way for the successful application of lab-scale electrodes in industrial electrolysis powered directly by renewable energy.</p

Theory, technology and practice of shale gas three-dimensional development: A case study of Fuling shale gas field in Sichuan Basin, SW China

In the Jiaoshiba block of the Fuling shale gas field, the employed reserves and recovery factor by primary well pattern are low, no obvious barrier is found in the development layer series, and layered development is difficult. Based on the understanding of the main factors controlling shale gas enrichment and high production, the theory and technology of shale gas three-dimensional development, such as fine description and modeling of shale gas reservoir, optimization of three-dimensional development strategy, highly efficient drilling with dense well pattern, precision fracturing and real-time control, are discussed. Three-dimensional development refers to the application of optimal and fast drilling and volume fracturing technologies, depending upon the sedimentary characteristics, reservoir characteristics and sweet spot distribution of shale gas, to form “artificial gas reservoir” in a multidimensional space, so as to maximize the employed reserves, recovery factor and yield rate of shale gas development. In the research on shale gas three-dimensional development, the geological + engineering sweet spot description is fundamental, the collaborative optimization of natural fractures and artificial fractures is critical, and the improvement of speed and efficiency in drilling and fracturing engineering is the guarantee. Through the implementation of three-dimensional development, the overall recovery factor in the Jiaoshiba block has increased from 12.6% to 23.3%, providing an important support for the continuous and stable production of the Fuling shale gas field

Corrigendum to “Bridging NiCo layered double hydroxides and Ni3S2 for bifunctional electrocatalysts: The role of vertical graphene” [Chem. Eng. J. 415 (2021) 129048](S1385894721006392)(10.1016/j.cej.2021.129048)

The authors regret errors in Tafel plots in Figs. 4C and 5C in the published article due to the inadvertent mistake of data import when plotting in the Origin software. Thus, Figs. 4C and 5C need corrections. Those corrections do not affect the discussion and conclusions of the original article. The updated Figures are shown as below. The authors would like to apologize for any inconvenience caused.</p