In this work, we investigate the effects of nanogrooves on heterogeneous ice nucleation (HIN) through molecular dynamics simulations. It is found that nanogrooves on a surface significantly alter the ice nucleation rate by more than 2 orders of magnitude. Depending on the width of the grooves, the nucleation rate can be enhanced or impeded compared with that on flat surfaces. For relatively large grooves, ice nucleation enhancement is observed when the effective groove width is a multiple of the ice lattice constant, for which ice crystal nucleus forms in the groove. For narrow grooves, strong confinements lead to the formation of solidlike layered structures, which may or may not enhance ice nucleation, depending on their structural match with ice crystal. The findings in this work provide critical information for surface designs in controlling HIN.
Technological developments showed that fuel cells are effective sources of power for medium-to large-scale backup power and vehicular applications (e.g., automobiles and buses). [4] In particular, fuel-cellpowered electric vehicles have a longer driving range and shorter refueling time than rechargeable battery-powered vehicles. For example, Toyota has reported that its hybrid fuel cell vehicle can drive up to 830 km powered by 5 kg of H 2 at a pressure of less than 700 bar. [5,6] In this Perspective, we analyze progress in the development of fuel cells fabricated from polymer electrolyte membranes, which run at relatively low temperature (60-90 °C), start up fast, and are portable, and have thus drawn much attention for their potential commercial applications. [7] Proton exchange membrane fuel cells (PEMFCs) have proven successful for transportation and power generation applications, owing to their high power output, compact design, and lightweight cells. Their high performance is due to their use of Nafion, a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer with outstanding chemical stability [8] and excellent proton (H + ) conductivity. [9] PEMFCs' high power output has been demonstrated in stationary, portable, and high-demand devices, and in consumer vehicles. [10][11][12] However, PEMFC membranes and catalysts are expensive, and this has hindered the broader adoption of PEMFC technology by the market. Specifically, PEMFC stacks (i.e., combinations of multiple PEMFCs) are expensive due to their requirement for platinum-group metal (PGM) catalysts and fluorocarbon membranes, which account for 40% and 11% of a cell's cost, respectively, and translate to high vehicle prices. [13,14] As a result, manufacturers are attempting to meet market demand for cheaper PEMFCs by lowering their content of PGM catalysts (or eschewing PGM catalysts entirely) and avoiding their use of fluorocarbon membranes. As an alternative to the use of H + in ion transport, the corresponding redox reactions of hydroxide (OH − ) ions have received attention. Fuel cells with OH − -transporting membranes are termed anion exchange membrane fuel cells (AEMFCs). The working principles of AEMFCs are slightly different from those of PEMFCs, but their overall redox bases are the same. In an AEMFC, water and oxygen are fed into the cathode for reduction to OH − , which then travel through the AEM to the anode to meet the fuel, H 2 , which is oxidized to generate electricity, with water as a byproduct. [15][16][17][18] In contrast to PEMFCs, AEMFCs use cationic Fuel cell technology is a clean way of generating energy and should enable carbon neutrality. However, although traditional proton exchange membrane fuel cells (PEMFCs) have made a commercial impact, their high cost hinders their wider adoption. Fuel cells that use anion exchange membranes (AEMs) are a promising alternative to PEMFCs, as they can achieve the same performance at a lower cost. In this Perspective, recent trends in the fabrication of polymer-based high-performance AEM...
Au–Pd core–shell nanoparticles can convert CO2 into CO with a high selectivity and mass activity due to the more balanced *COOH/*CO adsorption.
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