Abstract
For steady electroconversion to value-added chemical products with high efficiency, electrocatalyst reconstruction during electrochemical reactions is a critical issue in catalyst design ...strategies. Here, we report a reconstruction-immunized catalyst system in which Cu nanoparticles are protected by a quasi-graphitic C shell. This C shell epitaxially grew on Cu with quasi-graphitic bonding via a gas–solid reaction governed by the CO (g) - CO
2
(g) - C (s) equilibrium. The quasi-graphitic C shell-coated Cu was stable during the CO
2
reduction reaction and provided a platform for rational material design. C
2+
product selectivity could be additionally improved by doping
p
-block elements. These elements modulated the electronic structure of the Cu surface and its binding properties, which can affect the intermediate binding and CO dimerization barrier. B-modified Cu attained a 68.1% Faradaic efficiency for C
2
H
4
at −0.55 V (vs RHE) and a C
2
H
4
cathodic power conversion efficiency of 44.0%. In the case of N-modified Cu, an improved C
2+
selectivity of 82.3% at a partial current density of 329.2 mA/cm
2
was acquired. Quasi-graphitic C shells, which enable surface stabilization and inner element doping, can realize stable CO
2
-to-C
2
H
4
conversion over 180 h and allow practical application of electrocatalysts for renewable energy conversion.
Organogel‐based stretchable electronic conductors exhibit electrical conduction even under a large stretching deformation of 300% without electrochemical reactions at DC voltages. The resistance ...change with stretching is almost strain‐insensitive up to 50% strain and it remains at each deformation up to 1000 fatigue cycle. The polymeric conductive paths of PEDOT:PSS are well preserved during the mechanical deformation.
Low-temperature-processed perovskite solar cells (PSCs), especially those fabricated on flexible substrates, exhibit device performance that is worse than that of high-temperature-processed PSCs. One ...of the main reasons for the inferior performance of low-temperature-processed PSCs is the loss of photogenerated electrons in the electron collection layer (ECL) or related interfaces, i.e., indium tin oxide/ECL and ECL/perovskite. Here, we report that tailoring of the energy level and electron transporting ability in oxide ECLs using Zn2SnO4 nanoparticles and quantum dots notably minimizes the loss of photogenerated electrons in the low-temperature-fabricated flexible PSC. The proposed ECL with methylammonium lead halide MAPb(I0.9Br0.1)3 leads to fabrication of significantly improved flexible PSCs with steady-state power conversion efficiency of 16.0% under AM 1.5G illumination of 100 mW cm–2 intensity. These results provide an effective method for fabricating high-performance, low-temperature solution-processed flexible PSCs.
As the demand for soft and flexible devices steadily increases, the ionic applications demonstrated with gel materials have come under the spotlight. Here, stretchable and wearable ionic diodes ...(SIDs) made from polyelectrolyte hydrogels are introduced. Polyelectrolyte hydrogels are mechanically modified using methacrylated polysaccharides while preserving the ion‐permselectivity of poly(sulfopropyl acrylate) potassium salt (PSPA) and poly(acrylamidopropyltrimethylammonium chloride) (PDMAPAA‐Q), forming ionic copolymers. Then, SIDs composed of polyelectrolyte copolymer hydrogels are fabricated in VHB substrates as a stretchable and transparent insulating layer which is engraved by a laser. The SIDs show rectifying behaviors beyond the stretch of 3 with the aid of perfect adhesion between hydrogels and elastomeric substrates, and preserve their rectifications over hundreds of cycles. The operation of the SID is visualized by a wearable ionic circuit which rectifies ionic currents and lightens the LED under the forward bias during finger movements.
A stretchable ionic diode is demonstrated from polyelectrolyte hydrogels. Polyelectrolyte gels are mechanically modified with maintaining their own ion‐selective properties to generate a P–N junction. With the aid of perfect adhesion between the hydrogel materials and an elastomeric substrate, ionic diodes can rectify ionic currents under the applied stretch beyond 3.
As the technology of flexible electronics has remarkably advanced, the long-term reliability of flexible devices has attracted much attention, as it is an important factor for such devices in ...reaching real commercial viability. To guarantee the bending fatigue lifetime, the exact evaluation of bending strain and the change in electrical resistance is required. In this study, we investigated the bending strains of Cu thin films on flexible polyimide substrates with different thicknesses using monolayer and bilayer bending models and monitored the electrical resistance of the metal electrode during a bending fatigue test. For a thin metal electrode, the bending strain and fatigue lifetime were similar regardless of substrate thickness, but for a thick metal film, the fatigue lifetime was changed by different bending strains in the metal electrode according to substrate thickness. To obtain the exact bending strain distribution, we conducted a finite-element simulation and compared the bending strains of thin and thick metal structures. For thick metal electrodes, the real bending strain obtained from a bilayer model or simulation showed values much different from those from a simple monolayer model. This study can provide useful guidelines for developing highly reliable flexible electronics.
The distinguishing feature of a flexible electronic device is that it maintains its function even when the shape changes repeatedly. As the degree of integration of flexible devices increases, ...revealing failure mechanisms and extending the lifetime of the flexible devices are getting more difficult. One of the potential damage zones is the interface of heterogeneous material components, where strain can be localized due to the mismatch of mechanical properties. In this study, we investigate the mechanically reliable interconnect design of the flexible printed circuit board (FPCB) system in which the packaging chip is integrated. When the FPCB was bent, folding occurred at the edge of the packaging chip due to the high bending rigidity compared with the plastic substrate and resulted in high strain concentration. By introducing interconnect architecture that bypassed the strain concentration area around the packaging chip, mechanical damage of the interconnects was successfully reduced. Through finite element simulation, the strain applied to the interconnect crossing the strain-concentrated region was predicted to be 2 times larger than that bypassing the strain-concentrated region, from 8.32 to 4.64%. In addition, the strain gap of these two interconnects could be increased as the Young’s modulus mismatch between the packaging chip and the substrate increased. This study is expected to improve the design guidelines to mechanically reliable interconnects in highly integrated flexible electronics.
Graphical Abstract
Deformation behavior of the Ag nanowire flexible transparent electrode under bending strain is studied and results in a novel approach for highly reliable Ag nanowire network with mechanically welded ...junctions. Bending fatigue tests up to 500 000 cycles are used to evaluate the in situ resistance change while imposing fixed, uniform bending strain. In the initial stages of bending cycles, the thermally annealed Ag nanowire networks show a reduction in fractional resistance followed by a transient and steady‐state increase at later stages of cycling. SEM analysis reveals that the initial reduction in resistance is caused by mechanical welding as a result of applied bending strain, and the increase in resistance at later stages of cycling is determined to be due to the failure at the thermally locked‐in junctions. Based on the observations from this study, a new methodology for highly reliable Ag nanowire network is proposed: formation of Ag nanowire networks with no prior thermal annealing but localized junction formation through simple application of mechanical bending strain. The non‐annealed, mechanically welded Ag nanowire network shows significantly enhanced cyclic reliability with essentially 0% increase in resistance due to effective formation of localized wire‐to‐wire contact.
Fatigue behavior of the Ag nanowire flexible transparent electrode is investigated while monitoring resistance in situ. The Ag nanowire network has an excellent fatigue resistance due to the stretchability of the network as well as the limited dislocation activity of the metal nanowires. Further enhancement in fatigue resistance is achieved by using mechanically welded junctions instead of thermally locked‐in junctions.
Although cuprous oxide, Cu2O, has attracted attention as a promising p‐type semiconductor material for carbon dioxide reduction (CO2RR) photocatalysts, serious stability problems have always occurred ...due to photocorrosion. In this work, we fabricated hierarchical‐structured photocathodes with CuFeO2 on Cu2O nanorods by spray pyrolysis and oxygen‐controlled heat treatment to improve the stability of Cu2O from a thermodynamic perspective. Field‐emission scanning electron microscopy, field‐emission transmission electron microscopy and X‐ray diffraction confirmed that the Cu2O/CuFeO2 hierarchical nanorod structure was successfully fabricated. It was observed that the photocathodes show enhanced stability as the Fe content increases. Therefore, we report that the CuFeO2 layer enhances the stability of the Cu2O nanorod photocathode. A photocathode with a Cu : Fe atomic ratio of 1.52 : 1 has a current density of 1.1 mA/cm2 at 0.35 VRHE even after 10 linear voltage sweep repetitions, a decrease of only 8 % compared to the current density at the first sweep. Additionally, formate and acetate were produced during the CO2RR, exhibiting faradaic efficiencies (FEs) of 21.6 % and 68.6 %, respectively.
Strength through iron: Newly fabricated Cu2O/CuFeO2 hierarchical nanorods have been applied as a photocatalyst for carbon dioxide reduction. They show high stability and current density and the photocathodes show enhanced stability as the ratio of Fe increases.
•An 4D printed SMC actuator was fabricated using SMA and SMP with a FDM 3D printer.•A volume fraction of SMA:SMP of 1:5 showed the largest length change of 8 mm, and the most rapid response time of 4 ...s.•The reversible actuator mechanism explains the SMC actuation via each shape memory effect.•SMC showed potential application for stents and valve controllers via 3D printing technology to achieve customized designs.
A fused deposition modeling (FDM) tool was used to fabricate a shape memory composite (SMC) that combined a shape memory alloy (SMA) with a shape memory polymer (SMP). The SMA caused a shape memory effect due to a phase change between martensite and austenite phases, in turn due to a temperature change. Also, the SMP had a shape memory effect caused by changes in the proportions of hard and soft segments near the glass transition temperature (Tg). Usually, common SMAs and SMPs are not reversible, so these materials do not go back to their original shapes once they are deformed. In this study, we fabricated 4D printing actuator via reversible SMC actuations using 3D printing technology. Nylon 12 was used as the 3D printing material in filament form. Moreover, the volume fraction of SMA to SMP was varied to find the optimum ratio for good operation cycles. A volume fraction of SMA:SMP of 1:5 showed the largest length change, of 8 mm, and the most rapid response time, of 4 s in overall dimension of 140mm×10mm×1mm (length×width×thickness).Thus, the SMC showed promising results for the application of stents and valve controllers that could be manufactured by 3D printing technology.
As biological signals are mainly based on ion transport, the differences in signal carriers have become a major issue for the intimate communication between electrical devices and biological areas. ...In this respect, an ionic device which can directly interpret ionic signals from biological systems needs to be designed. Particularly, it is also required to amplify the ionic signals for effective signal processing, since the amount of ions acquired from biological systems is very small. Here, we report the signal amplification in ionic systems as well as sensing through the modified design of polyelectrolyte hydrogel-based ionic diodes. By designing an open-junction structure, ionic signals from the external environment can be directly transmitted to an ionic diode. Moreover, the minute ionic signals injected into the devices can also be amplified to a large amount of ions. The signal transduction mechanism of the ion-to-ion amplification is suggested and clearly verified by revealing the generation of breakdown ionic currents during an ion injection. Subsequently, various methods for enhancing the amplification are suggested.
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