Development of non-noble metal electrocatalysts for hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in acid is a great challenge for the development of polymer electrolyte membrane water electrolysis (PEMWE) and polymer electrolyte membrane fuel cells (PEMFC). Here, we report an efficient strategy for modulating the electron density of MoO2 by Ni doping to accelerate HER and HOR in acid. This is particularly important for PEMWE, PEMFC, and regenerative fuel cells. X-ray absorption spectroscopy demonstrates that Ni is doped by replacing Mo atoms in MoO2. Then Ni doping can lead to electron deficiency on neighboring O sites, which are induced to adsorb hydrogen and then increase the surface hydrogen coverage. Therefore, the doping of Ni can modulate the electron density of MoO2 for accelerating HER and HOR. Our results indicate that the incorporation of a high-electronegativity transition metal into MoO2 provides a new strategy for replacing Pt as an electrocatalyst for HER and HOR in acid.

Efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional electrocatalysts have been pursued for decades. Meanwhile, single metal atoms embedded in a two-dimensional material substrate (2D-substrate) have emerged as an outstanding catalyst. Herein, we report on computational ORR/OER efficiencies of a series of single atom catalyst systems, with a nitrogen-doped boron phosphide monolayer (N 3 -BP) as the 2D-substrate, and with Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rh, Pd, Ir, and Pt as the single-atom subject (M). In brief, our density functional theory results show that the overpotentials for ORR/OER are low for CoN 3 -BP, NiN 3 -BP, and PtN 3 -BP, with {η ORR ; η OER } of {0.36; 0.42 V}, {0.29; 0.44 V}, and {0.32; 0.25 V}, respectively. The relevant attributes such as the chemical stability of the 2D-substrate in the ORR/OER environments, immobilization of the single-atom subject on the 2D-substrate, and mechanisms of the ORR/OER activity and the catalyst recovery on the MN 3 -BP catalysts were carefully examined. The key to the comparative study is how the electronic states of the reaction center near the Fermi level of the catalytic system match the frontier orbitals of ORR/OER reaction intermediates. In short, our method predicts the ORR/OER catalytic efficiencies of novel catalysts via a single-atom/2D-substrate design strategy.

Long time coherent integration is a vital method for improving the detection ability of global navigation satellite system (GNSS)-based passive radar, because the GNSS signal is not radar-designed and its power level is very low. For aircraft detection, the large range cell migration (RCM) and Doppler frequency migration (DFM) will seriously affect the coherent processing of azimuth signals, and the traditional range match filter will also be mismatched due to the Doppler-intolerant characteristic of GNSS signals. Accordingly, the energy loss of 2-dimensional (2-D) coherent processing is inevitable in traditional methods. In this paper, a novel 2-D coherent integration processing and algorithm for aircraft target detection is proposed. For azimuth processing, a modified Radon Fourier Transform (RFT) with range-walk removal and Doppler rate estimation is performed. In respect to range compression, a modified matched filter with a shifting Doppler is applied. As a result, the signal will be accurately focused in the range-Doppler domain, and a sufficiently high SNR can be obtained for aircraft detection with a moving target detector. Numerical simulations demonstrate that the range-Doppler parameters of an aircraft target can be obtained, and the position and velocity of the aircraft can be estimated accurately by multiple observation geometries due to abundant GNSS resources. The experimental results also illustrate that the blind Doppler sidelobe is suppressed effectively and the proposed algorithm has a good performance even in the presence of Doppler ambiguity.

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