Influence of Crystal Structure on the Electrochemical Performance of A-Site-Deficient Sr\u3csub\u3e1-s\u3c/sub\u3eNb\u3csub\u3e0.1\u3c/sub\u3eCo\u3csub\u3e0.9\u3c/sub\u3eO\u3csub\u3e3-δ\u3c/sub\u3e Perovskite Cathodes

The creation of A-site cation defects within a perovskite oxide can substantially alter the structure and properties of its stoichiometric analogue. In this work, we demonstrate that by vacating 2 and 5% of Asite cations from SrNb0.1Co0.9O3-δ (SNC1.00) perovskites (Sr1-sNb0.1Co0.9O3-δ,s = 0.02 and 0.05; denoted as SNC0.98 and SNC0.95, respectively), a Jahn–Teller (JT) distortion with varying extents takes place, leading to the formation of a modified crystal lattice within a the perovskite framework. Electrical conductivity, electrochemical performance, chemical compatibility and microstructure of Sr1-sNb0.1Co0.9O3-δ as cathodes for solid oxide fuel cells were evaluated. Among SNC1.00, SNC0.98 and SNC0.95, SNC0.95 (P4/mmm symmetry (#123)) which exhibits a large JT distortion in conjunction with charge-ordering of cobalt (Co) shows the best oxygen reduction reaction (ORR) activity at low temperature while SNC0.98 (P4mm symmetry (#99)), which displays a local JT distortion, shows the poorest performance

Influence of Crystal Structure on the Electrochemical Performance of A-Site-Deficient Sr 1-xNb 0.1 Co 0.9 O 3-δ Perovskite Cathodes

The creation of A-site cation defects within a perovskite oxide can substantially alter the structure and properties of its stoichiometric analogue. In this work, we demonstrate that by vacating 2 and 5% of A-site cations from SrNb0.1Co0.9O3−δ (SNC1.00) perovskites (Sr1−sNb0.1Co0.9O3−δ, s = 0.02 and 0.05; denoted as SNC0.98 and SNC0.95, respectively), a Jahn–Teller (JT) distortion with varying extents takes place, leading to the formation of a modified crystal lattice within a the perovskite framework. Electrical conductivity, electrochemical performance, chemical compatibility and microstructure of Sr1−sNb0.1Co0.9O3−δ as cathodes for solid oxide fuel cells were evaluated. Among SNC1.00, SNC0.98 and SNC0.95, SNC0.95 (P4/mmm symmetry (#123)) which exhibits a large JT distortion in conjunction with charge-ordering of cobalt (Co) shows the best oxygen reduction reaction (ORR) activity at low temperature while SNC0.98 (P4mm symmetry (#99)), which displays a local JT distortion, shows the poorest performance

Natural manganese ores for efficient removal of organic pollutants via catalytic peroxymonosulfate-based advanced oxidation processes

Peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) for in situ persistent organic pollutant (POP) remediation in aqueous solutions can be a promising technology. However, this technology is constrained by its high toxicity and cost of metal oxide and non-metal catalysts for PMS activation. Here, we investigated the catalytic performance of a widely available natural mineral, manganese ore (MO), for PMS activation. A series of natural MO samples in an aqueous solution were prepared via the Fenton-like reaction. The samples\u27 crystalline structure, surface morphology, textural properties, and other surface characteristics of the selected MO were systematically characterized. The effects of PMS concentration and process parameters on the degradation performance of four chosen model pollutants, that is, phenol, tetrabromobisphenol A (TBBPA), rhodamine B (RhB), and methylene blue (MB), were evaluated. The experimental results showed that natural MO increased catalytic activity and enhanced the PMS oxidation processes, with 98%, 90%, and 75% removal efficiencies on phenol, TBBPA, and RhB, respectively, within 1.5 h. The reduction in the initial pH solution from 10 to 7 and the increase in temperature from 15 to 45°C enhanced the MB degradation rate (decolorization) by 55 and 46%, respectively, within 2 h. During the PMS activation process, SO4−, OH, and 1O2 species were generated, but only SO4− and OH radicals with strong oxidative potentials contributed to the catalytic degradation. The dissolved metals from the experiments were found well within the limit of drinking water standards, verifying that the MO + PMS catalytic system is suitable for commercial applications. This work provides insights into the development potential and prospects of using natural minerals for PMS activation and POP degradation, which can accelerate their industrial applications

Physicochemical and structural characterisation of oil palm trunks (OPT) hydrochar made via wet torrefaction

This study evaluates the effect of wet torrefaction of OPT under autogenous pressures at 3 different relatively low temperatures (i.e. 180, 200, and 220 oC) and extended residence times (i.e. 3, 6, 9, 12, 18, 24, 48, and 72 h) on the hydrochar's physical, chemical, and structural properties. Logarithmic-like increase of HHV profile was observed at the highest temperature of 220 oC, in which a plateau was reached at 24 h. Between temperature and residence time, temperature gave a more significant influence on the characteristics of the produced biochar. The HHV of the biomass sample increases from 16.4 MJ kg−1 in raw OPT to the highest HHV of 26.9 MJ kg−1 when torrefied at 220 oC for 72 h. Van Krevelen analysis shows dehydration was the primary reaction pathway that occurred during wet torrefaction of OPT at 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h. Decarboxylation dominates the reaction when temperature and residence time was increased to 220 oC for 24 h, respectively. Further increasing the residence time to 48 and 72 h at 220 oC promotes demethylation as the dominant reaction. FTIR analysis reveals that most hemicellulose and parts of cellulose decomposed when OPT was subjected to lower temperature and/or residence time (i.e. 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h). However, increasing temperature to 220 oC and beyond 24 h resulted in carbon-rich and lignin-dense hydrochar, which was observed in powder XRD results where graphite nitrate peak at 2θ of 7.4o appears. Morphology analysis reveals that most of the hemicellulose and cellulose-rich parenchyma was removed when subjected to wet torrefaction at 220 oC for 24 h. The formation of microspheres from the repolymerisation of 5-HMF was observed in large quantities in OPT hydrochar treated at 220 oC for 72 h. Inorganic elemental analysis shows that wet torrefaction of OPT effectively removes K and Cl from the biomass. The removal of K increased with increased temperature, which may partially resolve the corrosion problems in combustion reactions related to silicate deposition. OPT hydrochar from WT under autogenous condition and relatively low temperature exhibits much more improved fuel properties compared to raw OPT

Thermogravimetric analysis of face mask waste: Kinetic analysis via iso-conversional methods

The surge of face mask waste in response to the global pandemic has proven to be a liability to the environment. Microfibers from plastic constituents of the face mask would cause microplastic pollution in the water bodies. Fortunately, these waste could be converted into renewable source of energy via thermochemical method, i.e. pyrolysis. However, the studies on the thermal decomposition of face masks and their kinetic mechanisms are not well-established. The aim of this paper focuses on the prospects of pyrolysis at low to high heating rates ranging from 10 °C min-1 to 100 °C min-1, to cater for the slow pyrolysis and fast pyrolysis modes. Following this, the thermal degradation behaviour of the face mask waste was studied via thermogravimetric analysis which determined the single peak temperature degradation range at 218 to 424 °C at 10 °C min-1, and maximum degradation rate was determined at 172.51 wt.% min-1 at 520 °C, with heating rate of 100 °C min-1. Flynn-Wall-Ozawa (FWO) and Starink method was employed to determine the average activation energy and average pre-exponential factor of the pyrolysis process of face mask waste. i.e., 41.31 kJ mol-1 and 0.9965, 10.43 kJ mol-1 and 0.9901 for FWO and Starink method, respectively

Roadmap for Sustainable Mixed Ionic‐Electronic Conducting Membranes

Mixed ionic‐electronic conducting (MIEC) membranes have gained growing interest recently for various promising environmental and energy applications, such as H₂ and O₂ production, CO₂ reduction, O₂ and H₂ separation, CO₂ separation, membrane reactors for production of chemicals, cathode development for solid oxide fuel cells, solar‐driven evaporation and energy‐saving regeneration as well as electrolyzer cells for power‐to‐X technologies. The purpose of this roadmap, written by international specialists in their fields, is to present a snapshot of the state‐of‐the‐art, and provide opinions on the future challenges and opportunities in this complex multidisciplinary research field. As the fundamentals of using MIEC membranes for various applications become increasingly challenging tasks, particularly in view of the growing interdisciplinary nature of this field, a better understanding of the underlying physical and chemical processes is also crucial to enable the career advancement of the next generation of researchers. As an integrated and combined article, it is hoped that this roadmap, covering all these aspects, will be informative to support further progress in academics as well as in the industry‐oriented research toward commercialization of MIEC membranes for different applications

Oxygen reduction reaction activity and structure of La-based perovskite oxides

1706 files in 35 folders, containing 388MB. Comprises plots, figures, and manuscripts. The data contains x-ray diffraction patterns and electrochemical data of lanthanum based perovskite oxides (e.g. 9 different perovskite compositions e.g. LaNiO3, LaCoO3, LaFeO3, LaMnO3, LaCrO3, LaNi0.5Co0.5O3 and LaNi0.5Fe0.5O3, LaNi0.5Mn0.5O3 and LaNi0.5Cr0.5O3) characterized using rotating ring disk electrodes.<br /

Oxygen Selective Barium Bismuth based Perovskite Membranes

This thesis focused on the research and development of novel dense perovskite membranes for oxygen separation from air. Owing to the mixed ionic-electronic conducting (MIEC) properties of perovskite materials, oxygen ionic transport takes place at high temperatures generally in excess of 600oC, resulting in the production of pure oxygen. Despite the attractiveness of this technology, the oxygen fluxes are still limited at temperatures below 850oC, mainly attributed to low oxygen ionic diffusion. To address this problem, the research community has worked intensively on the compositional tailoring of perovskite materials with ABO3-d structure. These perovskite materials have the capability to incorporate different cation types namely A/A’ and/or B/B’ in their A-site and B-site leading to different A1-xA’xB1-xB’xO3-d compounds with specific structures and properties. Examples include (La,Sr)(Co,Fe)O3-d parent compounds and a large array of doping using various different cations, e.g. Ba, Ca, Sr, Na, La onto A-site of LaCo0.8Fe0.2O3-d; Cu, Ni, Co, Fe, Mn, Cr onto B-site of La0.6Sr0.4CoO3-d; Ba onto A-site of SrCo0.8Fe0.2O3-d; La, Nd, Sm, Gd onto A-site of SrCoO3-d and Ti and Bi onto B-site and A-site of SrFeO3-d. In this thesis, barium was selected as the base material for A-site cation in the perovskite lattices due to its fixed valence cation, Ba2+ and large ionic radius, 1.60Å which favours the creation of large lattice spacing and higher freedom of oxygen ionic movements. To complement barium, bismuth was chosen as a cation dopant since it has ionic radius variability at different valence states (Bi3+ and Bi5+) and coordination numbers which allowed flexible incorporation of bismuth in A-site and/or B-site. Hence, this work takes the advantage of these combined features of barium and bismuth to manipulate the perovskite structure towards favourable oxygen transport properties. This can be achieved through the fixed placement of barium in A-site in conjunction with flexible bismuth position in perovskite lattices. The first postulation of this thesis relates to the bismuth incorporation into perovskite lattice of barium-based perovskite oxides aiming at improving the ionic transport and oxygen fluxes at intermediate temperatures (650-850oC). This postulation is based on the superior ionic transport properties of bismuth. To test the first postulation, barium-bismuth perovskite oxides with different molar ratios of BiO1.5 to BaO (z), where z varied between 0.5-3, were investigated. It was found that barium-rich perovskite oxide of z=0.86, BaBi0.86O2.29 with slight deviation from z=1 showed the optimised oxygen fluxes of 1.2 ml cm-2 min-1. This was attributed to a higher sintering temperature of 1080oC for a compound of z=0.86 instead of 1000oC for a compound of z=1. Nevertheless, due to the insufficient amount of defects for high ionic diffusion, barium-bismuth perovskite oxides did not achieve optimum performance below 850oC. To that end, incorporating complementary metal oxides were deemed necessary to improve the membrane performance. The second postulation in this thesis was that iron addition onto barium-bismuth perovskite oxides provides better structural stability for barium-bismuth-iron perovskite oxides due to iron’s reduction tolerant properties. This postulation was verified by investigating barium-bismuth-iron perovskite oxides within the family of [Ba2−3xBi3x−1][Fe2xBi1−2x]O2+3x/2 with x between 0.17-0.60. It was found that upon increasing x from 0.33 to 0.60, the structure of these compounds changed from cubic to tetragonal and then to hexagonal. Compounds with x=0.33-0.40 exhibited the highest oxygen fluxes attributed to the cubic structure formation. While barium-bismuth-iron perovskite oxides delivered better structural stability with respect to barium-bismuth perovskite oxides, the optimised compound (x=0.33, [Ba][Fe0.67Bi0.33]O2.5) delivered low oxygen fluxes of 0.59 ml cm-2 min-1. Hence, the incorporation of iron decreased the oxygen flux by 50.83% as compared to the best composition of barium-bismuth perovskite oxides. In other words, the incorporation of iron in the barium-bismuth perovskite lattice reduced oxygen ionic transport, though relatively better structural stability was obtained. In addition, structure transition phenomena were found for compounds of x=0.55 and 0.66. The third postulation in this thesis was that bismuth doped barium-scandium-cobalt perovskite oxides enhanced the oxygen fluxes below 850oC. This postulation was envisaged based on the partial substitution of barium or cobalt on a perovskite compound BaSc0.1Co0.9O3-d with bismuth. This work aimed at using bismuth to reduce the ionic radius discrepancy between Ba and Sc/Co and thus ensuring the attainment of cubic structure below 850oC. Cobalt was utilized as the main component in the B-site cation to boost the oxygen permeation properties of the resultant perovskite oxides while scandium was added in small proportions to enhance the crystal structural stability and electrical conductivity as well as to counteract cobalt’s reducibility. A notable point discovered here is that a low amount of bismuth doping, e.g. less than or equal to 10 mole % stabilised the cubic structure. As a result, oxygen fluxes in these compounds increased up to two orders of magnitude between 650-850oC when compared to a non-doped compound. It was further demonstrated that nominal B-site doping was more beneficial to oxygen permeability with respect to nominal A-site doping. In particular, the optimised composition of BaBi0.05Sc0.1Co0.85O3-d delivered very high fluxes of 2.17 ml cm-2 min-1 at 950oC. Structure transition phenomena from non-cubic to cubic structure were also observed for non-doped compound (BaSc0.1Co0.9O3-d) and A-site doped compounds with 20 and 30 mole % of bismuth. A final contribution of this thesis was the development of the hollow fibre membranes with the optimised composition of barium-bismuth-scandium-cobalt perovskite oxide, BaBi0.05Sc0.1Co0.85O3-d, using a combined phase inversion and sintering technique. The hollow fibre membranes showed for the first time the achievement of very high oxygen fluxes e.g. 11.34 ml cm-2 min-1 at 950oC, in excess of target values for air separation units of 10 ml cm-2 min-1. This work further showed the effect of sweep gas flow rate on the oxygen permeances of BBSC hollow fibres, particularly above 800oC. This finding demonstrates that high oxygen fluxes were achieved only at high sweep gas flow rates of 150 ml min-1. For temperatures at or below 800oC, the oxygen flux was independent of the sweep gas flow rate, thus indicating the limitations imposed by oxygen ionic bulk diffusion and surface reaction. Through a compositional tailoring approach, this thesis has demonstrated the potential of barium-bismuth based perovskite oxides in advancing oxygen transport membrane technologies

Decontamination of hazardous substances from solid matrices and liquids using supercritical fluids extraction : a review

Supercritical fluid has been adopted as an extraction media to remove various kinds of substances from distinct types of solid matrices since three decades ago. Compared to conventional extraction mode, supercritical fluid extraction technology is preferred because of the flexibility in adjusting its dissolving power and inherent elimination of organic solvent which means reducing time and money needed for subsequent purification. Utilization of this method as an environmental remedial technology, however, has become a trend only after its accomplishment in analytical chemistry was acknowledged. This review tries to summarize in a comprehensive manner the multitude aspects involved in hazardous compounds removal from miscellaneous class of environmental matrices. The industrial adsorbent regeneration using supercritical fluid technology is also discussed. Although, this technology has been successfully realized for environmental remediation in laboratory and on pilot-plant scale, its commercialization attempts still lack significant technology improvement in order to reach the economic feasibility