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Oxygen is the most abundant element in the Earth's crust. The oxygen reduction reaction (ORR) is also the most important reaction in life processes and energy converting/storage systems. Developing techniques toward high-efficiency ORR remains highly desired and a challenge. Here, we report a N-doped carbon (NC) encapsulated CeO/Co interfacial hollow structure (CeO-Co-NC) via a generalized strategy for largely increased oxygen species adsorption and improved ORR activities. First, the metallic Co nanoparticles not only provide high conductivity but also serve as electron donors to largely create oxygen vacancies in CeO. Second, the outer carbon layer can effectively protect cobalt from oxidation and dissociation in alkaline media and as well imparts its higher ORR activity. In the meanwhile, the electronic interactions between CeO and Co in the CeO/Co interface are unveiled theoretically by density functional theory calculations to justify the increased oxygen absorption for ORR activity improvement. The reported CeO-Co-NC hollow nanospheres not only exhibit decent ORR performance with a high onset potential (922 mV vs RHE), half-wave potential (797 mV vs RHE), and small Tafel slope (60 mV dec) comparable to those of the state-of-the-art Pt/C catalysts but also possess long-term stability with a negative shift of only 7 mV of the half-wave potential after 2000 cycles and strong tolerance against methanol. This work represents a solid step toward high-efficient oxygen reduction.

Designing low-cost and highly efficient bifunctional electrocatalysts for compatible integration with the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) for overall water splitting is critical but challenging.

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Graphene can be utilized in designing adjustable terahertz (THz) devices due to its variability of sheet conductivity. In this paper, a broadband adjustable graphene absorber operating at THz frequencies is proposed. By changing the Fermi level of the graphene from 0 eV–1 eV, the absorption relative bandwidth and absorption rate can be adjusted from 20%–90.32% and from 0–100%, respectively. The Fermi level of the graphene can be adjusted actively by adjusting the bias voltage on the graphene layer or by chemical doping, which enables us to electrically or chemically control the absorption performance flexibly. We use the multi-reflection interference theory to investigate the physical insight of the proposed absorber under normal incidence and oblique incidence. This paper is the first to interpret oblique incidence using the multi-reflection interference theory. From this, we can infer the value of effective permittivity of the absorber under oblique incidence, which provides great help for the design of an absorber. The calculated and simulated results are in excellent agreement.