• Energy Research

B/N/P co-doped biomass carbons with optimized pore structure and electrical conductivity exhibited supervisor electrochemical performance in supercapacitors and sodium-ion batteries.

Abstract We herein report the synthesis of heteroatoms doped, high surface area microporous activated carbons (AC) by utilisation of Coca Cola® as a potential source of waste biomass, for applications as CO2 adsorbent and electrodes of supercapacitors. N, S dual doped carbon spheres are firstly obtained by hydrothermal treatment of Coca Cola® and then thermally activated by either KOH or ZnCl2. The resulting KOH activated carbon material (CMC-3) exhibits extremely high adsorption capability for CO2 with 5.22 mmol g−1 at 25 °C and 1 atm, one of the highest values ever recorded for a carbonaceous material. On the other hand, ZnCl2 activated carbon material (CMC-2) performs excellently as an electrode for supercapacitor, exhibiting very high specific capacitance of 352.7 F g−1 at a current density of 1 A g−1 in 6 M KOH electrolyte, which again is one of the highest values recorded for a biomass derived AC. Coca Cola® has high content in carbon as sugars, provides in-situ doping of O, N and S and has constant composition, as opposed to other conventional biomass materials, making it an attractive and cheap alternative for synthesis of high performance AC for environmental and energy storage purposes.

AbstractThe electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental processes in a range of energy conversion devices such as fuel cells and metal–air batteries. ORR and OER both have significant activation barriers, which severely limit the overall performance of energy conversion devices that utilize ORR/OER. Meanwhile, ORR is another very important electrochemical reaction involving oxygen that has been widely investigated. ORR occurs in aqueous solutions via two pathways: the direct 4-electron reduction or 2-electron reduction pathways from O2 to water (H2O) or from O2 to hydrogen peroxide (H2O2). Noble metal electrocatalysts are often used to catalyze OER and ORR, despite the fact that noble metal electrocatalysts have certain intrinsic limitations, such as low storage. Thus, it is urgent to develop more active and stable low-cost electrocatalysts, especially for severe environments (e.g., acidic media). Theoretically, an ideal oxygen electrocatalyst should provide adequate binding to oxygen species. Transition metals not belonging to the platinum group metal-based oxides are a low-cost substance that could give a d orbital for oxygen species binding. As a result, transition metal oxides are regarded as a substitute for typical precious metal oxygen electrocatalysts. However, the development of oxide catalysts for oxygen reduction and oxygen evolution reactions still faces significant challenges, e.g., catalytic activity, stability, cost, and reaction mechanism. We discuss the fundamental principles underlying the design of oxide catalysts, including the influence of crystal structure, and electronic structure on their performance. We also discuss the challenges associated with developing oxide catalysts and the potential strategies to overcome these challenges.

Dense oxygen ion–conducting ceramic membranes with CO2 resistance can promote many advanced applications such as membrane reactors for green chemical synthesis and oxy‐fuel combustion for clean energy delivery. The state‐of‐the‐art perovskite oxide membranes are characterized by their high O2 flux but low stability in a CO2‐containing atmosphere. To solve this problem, dual‐phase membranes have captured the imagination of researchers. Herein, a novel dual‐phase hollow fiber membrane with a composition of 40 wt% Ce0.9Gd0.1O2–δ (GDC)–60 wt% La2NiO4+δ (LNO) is developed via a combined phase inversion sintering process. During the high temperature treatment, La‐doping behavior is observed with La leaching out from the LNO phase and diffusing into the GDC phase. This dual phase membrane displays the O2 flux of 1.47 at 950 °C, which is reduced by 10% to 1.31 mL min−1 cm−2 when the sweep gas is switched from helium to pure CO2. Such minor O2 flux reduction is due to the strong CO2 adsorption on membrane surface occupying the O2 vacancies without permanent membrane damage, which is fully eliminated by an inert gas purge. Such a robust dual‐phase membrane exhibits the potential to overcome the low stability problem under the CO2‐containing atmosphere.