Biodiesel production from waste cooking oil (WCO) provides an alternative energy means of producing liquid fuels from biomass for various uses. Biodiesel production by recycling WCO and methanol in the presence of calcium oxide (CaO) nano-catalyst offers several benefits such as economic, environmental and waste management. A nano-catalyst of CaO was synthesized by thermal-decomposition method and calcinated at 500 °C followed by characterization using x-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The XRD results revealed nano-scale crystal sizes at high purity, with a mean particle size of ~29 nm. The SEM images exhibited morphology of irregular shapes and porous structure of the synthesized nanocatalysts. The highest conversion of WCO to biodiesel was estimated to be 96%, at optimized experimental conditions i.e., 50 °C, 1:8 WCO oil to methanol ratio, 1% by weight of catalyst loading rate and 90 minutes reaction time, which is among few highest conversions reported so far. Biodiesel properties were tested according to the American (ASTM D6571) fuel standards. All reactions are carried-out under atmospheric pressure and 1500 rpm of agitation.

The effects of Li2CO3 like species originating from reactions between CO2 and Li2O2 at the cathode of non-aqueous Li-air batteries were studied by density functional theory (DFT) and galvanostatic charge-discharge measurements. Adsorption energies of CO2 at various nucleation sites on a stepped (11̅00) Li2O2 surface were determined and even a low concentration of CO2 effectively blocks the step nucleation site and alters the Li2O2 shape due to Li2CO3 formation. Nudged elastic band calculations show that once CO2 is adsorbed on a step valley site, it is effectively unable to diffuse and impacts the Li2O2 growth mechanism, capacity, and overvoltages. The charging processes are strongly influenced by CO2 contamination, and exhibit increased overvoltages and increased capacity, as a result of poisoning of nucleation sites: this effect is predicted from DFT calculations and observed experimentally already at 1% CO2. Large capacity losses and overvoltages are seen at higher CO2 concentrations.

The formation and oxidation of the main discharge product in non-aqueous secondary Li-O 2 batteries, i.e. Li ) O ) , has been studied intensively, but less attention has been given to the formation of cathode electrolyte interfaces (CEI), which can significantly influence the performance of the Li-O 2 battery. Here, we apply density functional theory with the Hubbard U correction (DFT+U) and non-equilibrium Green's function (NEGF) methods to investigate the role of Li ) O ) @Li ) CO , interface layers on the ionic and electronic transport properties at the oxygen electrode. We show that, e.g., lithium vacancies accumulate at the peroxide part of the interface during charge, reducing the coherent electron transport by 2-3 orders of magnitude compared to pristine Li ) O ) . During discharge Li ) O ) @Li ) CO , interfaces may, however, provide an alternative inplane channel for fast electron polaron hopping that could improve the electronic conductivity and ultimately increase the practical capacity in non-aqueous Li-O 2 batteries.

In this report, the utilization of mixed methanol–ethanol system for the production of biodiesel from waste cooking oil (WCO) using enhanced eggshell-derived calcium oxide (CaO) nano-catalyst was investigated. CaO nano-catalyst was produced by calcination of eggshell powder at 900 °C and followed by hydration-dehydration treatment to improve its catalytic activity. The particle size, morphology, and elemental composition of a catalyst were characterized by using XRD, SEM, and EDX techniques, respectively. After hydration-dehydration the shape of a catalyst was changed from a rod-like to honeycomb-like porous microstructure. Likewise, average particle size was reduced from 21.30 to 13.53 nm, as a result, its surface area increases. The main factors affecting the biodiesel yield were investigated, accordingly, an optimal biodiesel yield of 94% was obtained at 1:12 oil to methanol molar ratio, 2.5 wt% catalyst loading, 60 °C, and 120-min reaction time. A biodiesel yield of 88% was obtained using 6:6 equimolar ratio of methanol to ethanol, the yield even increased to 91% by increasing the catalyst loading to 3.5 wt%. Moreover, by slightly increasing the share of methanol in the mixture, at 8:4 ratio, the maximum biodiesel yield could reach 92%. Therefore, we suggest the utilization of methanol–ethanol mixture as a reactant and eggshell-derived CaO as a catalyst for enhanced conversion of WCO into biodiesel. It is a very promising approach for the development of low-cost and environmentally friendly technology. Properties of the biodiesel were also found in good agreement with the American (ASTM D6571) fuel standards.

The Na-O system holds great potential as a low-cost, high-energy-density battery, but under normal operating conditions, the discharge is limited to sodium superoxide (NaO), whereas the high-capacity peroxide state (NaO) remains elusive. Here, we apply density functional theory calculations with an improved error-correction scheme to determine equilibrium potentials and free energies as a function of temperature for the different phases of NaO and NaO, identifying NaO as the thermodynamically preferred discharge product up to ∼120 K, after which NaO is thermodynamically preferred. We also investigate the reaction mechanisms and resulting electrochemical overpotentials on stepped surfaces of the NaO and NaO systems, showing low overpotentials for NaO formation (η = 0.14 V) and depletion (η = 0.19 V), whereas the overpotentials for NaO formation (η = 0.69 V) and depletion (η = 0.68 V) are found to be prohibitively high. These findings are in good agreement with experimental data on the thermodynamic properties of the Na O species and provide a kinetic explanation for why NaO is the main discharge product in Na-O batteries under normal operating conditions.