Hierarchical Cu−Sn core/shell nanowire arrays were built on 3‐dimensional macroporous Ni foams through a two‐step deposition, annealing, and electroreduction treatment. Cu was electroplated on Ni foam substrates and the sample was annealed at 500 °C followed by electroreduction, producing Cu nanowires of 150 nm diameter in arrays on the skeleton of Ni foams. Sn nanoparticles of 14–80 nm were then chemically deposited on Cu nanowires in clusters and a second annealing treatment at 200 °C followed by electroreduction re‐organized the clusters into a SnxO/Sn shell of 8 nm thickness. Creating such a Sn shell on Cu nanowires suppressed faradaic efficiencies for H2 evolution from 55.7 to 10.1 % and for HCOOH formation from 13.2 to 2.0 % and enhanced CO generation from 32.0 to 90.0 % at an applied potential of −0.8 V (vs. RHE). The faradaic efficiency for CO production remained almost constant at 90.0–91.4 % with total current densities of −13.2 to −19.3 mA cm−2 between −0.8 and −1.2 V (vs. RHE).
Nanostructure and crystallinity of transition metals play an important role in catalyzing carbon dioxide electroreduction (CO2ER) where Cu is a typical electrocatalyst with a wide variety of products and Pb has a high overpotential for H2 evolution and is selective toward formic acid. In this study, 3D hierarchical nanostructures of Cu–Pb catalyst are prepared by a two‐step electrodepositing–annealing–electroreduction approach (EAE). Cu nanowires (Cu NWs) of 200–400 nm diameter are built on the surface of commercial nickel foam substrates through an EAE step. Then, Pb nanoparticles with diameter of 5–10 nm are uniformly created on the surface of Cu NWs by a second EAE step. The nanostructural Cu–Pb electrodes catalyze CO2ER at a current density of −9.35 mA cm−2 (at −0.93 V vs reversible hydrogen electrode (RHE)). The H2 evolution is suppressed by 35.6% and CO and HCOOH are enhanced by 29.6% and 9.2%, respectively, as compared with Cu NWs. The protocol proposed in this study provides a simple and straightforward approach for preparing high‐performance, hierarchical nanostructures of Cu–Pb bimetal catalyst for CO2ER.
Core Ideas
Coupling SWAP with PEST, soil moisture and ET are included in inverse modeling of soil water flow.
Multi‐objective optimization could improve model predictions and reduce parameter uncertainty.
Observation errors and frequency and spatial arrangement impact predictions and uncertainty.
The accurate estimation of soil hydraulic properties is an important part of the application of hydrological models for quantifying water transport in the vadose zone. Various inverse models have been developed to solve hydraulic properties optimization problems, and the accuracy of the results obtained by different algorithms is still debated because of the inherent ill‐posedness of such problems. In this study, we coupled an agrohydrological Soil–Water–Atmosphere–Plant (SWAP) model with an independent parameter estimation program (PEST) to calibrate the soil hydraulic parameters and investigate the uncertainty in the parameter estimations. The objectives of this study were to assess to what extent the SWAP model can be calibrated from a single observation (only soil moisture, θ) and further to investigate whether involving additional evapotranspiration fluxes including actual evapotranspiration (ETa), actual evaporation (Ea), or actual transpiration (Ta) can lead to an improvement in model predictions and a reduction in parameter uncertainty. Extensive synthetic experiments were conducted to achieve the objectives. Both double (winter wheat [Triticum aestivum L.]–summer maize [Zea mays L.]) and single (only winter wheat or only summer maize) cropping systems were considered in the multi‐objective optimizations. The results indicate that although the addition of evapotranspiration fluxes does not necessarily improve the accuracy of the soil moisture prediction, it can reduce the parameter uncertainty for both single‐ and double‐cropping systems. Moreover, the parameter estimation of the topsoil layer could greatly benefit from the addition of Ea, whereas the addition of Ta could help reduce the parameter uncertainty of the lower layers.
There are several attempts to achieve efficient hydrogen storage. In this article, we introduce four main methods: conventional tank storage, metal and alloys hydrides storage, polymeric materials storage and carbon nanomaterials storage. We illustrate the advantages, disadvantages and current research process of each methods.
The development of efficient metal catalysts for in situ hydrogenation of CO 2 in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO 2 in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO 2 was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO 2 in aqueous bicarbonate solutions.
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