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  1. Low-temperature direct ammonia fuel cells (DAFCs) use carbon-neutral ammonia as a fuel, which has attracted increasing attention recently due to ammonia's low source-to-tank energy cost, easy transport and storage, and wide availability. However, current DAFC technologies are greatly limited by the kinetically sluggish ammonia oxidation reaction (AOR) at the anode. Herein, we report an AOR catalyst, in which ternary PtIrZn nanoparticles with an average size of 2.3 ± 0.2 nm were highly dispersed on a binary composite support comprising cerium oxide (CeO 2 ) and zeolitic imidazolate framework-8 (ZIF-8)-derived carbon (PtIrZn/CeO 2 -ZIF-8) through a sonochemical-assisted synthesis method. The PtIrZnmore »alloy, with the aid of abundant OH ad provided by CeO 2 and uniform particle dispersibility contributed by porous ZIF-8 carbon (surface area: ∼600 m 2 g −1 ), has shown highly efficient catalytic activity for the AOR in alkaline media, superior to that of commercial PtIr/C. The rotating disk electrode (RDE) results indicate a lower onset potential (0.35 vs. 0.43 V), relative to the reversible hydrogen electrode at room temperature, and a decreased activation energy (∼36.7 vs. 50.8 kJ mol −1 ) relative to the PtIr/C catalyst. Notably, the PtIrZn/CeO 2 -ZIF-8 catalyst was assembled with a high-performance hydroxide anion-exchange membrane to fabricate an alkaline DAFC, reaching a peak power density of 91 mW cm −2 . Unlike in aqueous electrolytes, supports play a critical role in improving uniform ionomer distribution and mass transport in the anode. PtIrZn nanoparticles on silicon dioxide (SiO 2 ) integrated with carboxyl-functionalized carbon nanotubes (CNT–COOH) were further studied as the anode in a DAFC. A significantly enhanced peak power density of 314 mW cm −2 was achieved. Density functional theory calculations elucidated that Zn atoms in the PtIr alloy can reduce the theoretical limiting potential of *NH 2 dehydrogenation to *NH by ∼0.1 V, which can be attributed to a Zn-modulated upshift of the Pt–Ir d-band that facilitates the N–H bond breakage.« less
  2. ABSTRACT We investigate the deformation processes during the 2019 Ridgecrest earthquake sequence by combining Global Navigation Satellite Systems, strong-motion, and Interferometric Synthetic Aperture Radar datasets in a joint inversion. The spatial complementarity of slip between the Mw 6.4 foreshock, Mw 7.1 mainshock, and afterslip suggests the importance of static stress transfer as a triggering mechanism during the rupture sequence. The coseismic slip of the foreshock concentrates mainly on the east-northeast–west-southwest fault above the hypocenter at depths of 2–8 km. The slip distribution of the mainshock straddles the region above the hypocenter with two isolated patches located to the north-northwest and south-southeast, respectively. Themore »geodetically determined moment magnitudes of the foreshock and mainshock are equivalent to moment magnitudes Mw 6.4 and 7.0, assuming a rigidity of 30 GPa. We find a significant shallow slip deficit (>60%) in the Ridgecrest ruptures, likely resulting from the immature fault system in which the sequence occurred. Rapid afterslip concentrates at depths of 2–6 km, surrounding the rupture areas of the foreshock and mainshock. The ruptures also accelerated viscoelastic flow at lower-crustal depths. The Garlock fault was loaded at several locations, begging the question of possible delayed triggering.« less
  3. SUMMARY Inverse problems play a central role in data analysis across the fields of science. Many techniques and algorithms provide parameter estimation including the best-fitting model and the parameters statistics. Here, we concern ourselves with the robustness of parameter estimation under constraints, with the focus on assimilation of noisy data with potential outliers, a situation all too familiar in Earth science, particularly in analysis of remote-sensing data. We assume a linear, or linearized, forward model relating the model parameters to multiple data sets with a priori unknown uncertainties that are left to be characterized. This is relevant for global navigationmore »satellite system and synthetic aperture radar data that involve intricate processing for which uncertainty estimation is not available. The model is constrained by additional equalities and inequalities resulting from the physics of the problem, but the weights of equalities are unknown. We formulate the problem from a Bayesian perspective with non-informative priors. The posterior distribution of the model parameters, weights and outliers conditioned on the observations are then inferred via Gibbs sampling. We demonstrate the practical utility of the method based on a set of challenging inverse problems with both synthetic and real space-geodetic data associated with earthquakes and nuclear explosions. We provide the associated computer codes and expect the approach to be of practical interest for a wide range of applications.« less
  4. Micro-supercapacitor is a member of the miniaturized energy storage device family, which offers great advantages on power density and life span. However, the limited device capacitance and narrow voltage window limit its energy density, hindering its application. In the present work, a novel micro-pseudocapacitor (MPC) constructed via the facile extrusion-based 3D printing technique has been demonstrated to deliver efficient charge storage with high device capacitance and moderate voltage window. Such an asymmetric MPC is constructed with 3D-printing-enabled asymmetric interdigitated cellular microelectrodes; in which, one is Ni–Co–O nanosheets grown on macroporous 3D reduced GO (3DG) microelectrode and the other is MnOmore »2 nanosheets grown on 3DG. Such an MPC offers facilitated fast electron transport, ionic diffusion, large number of active sites and desired porosity for electrolyte penetration. The asymmetric MPC shows a high specific capacity of 500 mC cm −2 , an energy density of 90 μW h cm −2 and a voltage window of 1.3 V. A device cycling stability with 10 000 charge and discharge cycles is also achieved for the as-fabricated asymmetric MPCs. These encouraging results may open a new avenue to design and fabricate state-of-the-art miniaturized electrochemical energy storage devices with customized geometries.« less