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.
The enhancement of the electrical conductivity by doping is important in hematite (α-Fe(2)O(3)) photoanodes for efficient solar water oxidation. However, in spite of many successful demonstrations ...using extrinsic dopants, such as Sn, Ti, and Si, the achieved photocurrent is still lower than the practical requirement. There is still lack of our understanding of how intrinsic oxygen defects can change the photocurrent and interact with the extrinsic dopants. In this study, we systematically investigate the interplay of oxygen vacancies and extrinsic Sn dopants in the context of photoanodic properties. As a result, we demonstrate that the controlled generation of oxygen vacancies can activate the photoactivity of pure hematite remarkably and further enhance the Sn doping effects synergistically. Furthermore, the correlated behavior of oxygen vacancies and Sn dopants is closely linked to the variation of electrical conductance and results in the optimum concentration region to show the high photocurrent and low onset voltage.
Electrocatalysts for CO
2
electroreduction require not only high-performance active materials to control the series reaction but also conductive and durable supports to ensure long-term stability ...under harsh operating conditions. Instead of conventional heterogeneous catalysts made by attaching metal on supports, we manufactured a self-formed tandem catalyst designed for a cascade electroreduction of CO
2
to C
2
H
4
. Using oxygen partial pressure-controlled calcination, electrospun copper acetate/polyacrylonitrile nanofibers were successfully transformed into porous carbon nanofibers consisting of doped N and metallic Cu particles. Doped nitrogen atoms adjacent to Cu atoms trigger the reaction by increasing the amount of CO* on the Cu surfaces, which lowers the energy required for CO dimerization that is used for C
2
H
4
production. The Cu-embedded N-doped carbon nanofibers exhibit a C
2
H
4
faradaic efficiency of 62% at a potential of −0.57 V
vs.
RHE with high current density of 600 mA cm
−2
and excellent long-term stability. DFT calculations suggest that the lowered overpotential originates from the decreased CO dimerization energy barrier due to the doped N triggering CO production around the Cu particles.
Cu acetate/PAN nanofibers were transformed into porous C nanofibers with doped N and Cu particles,
via
O
2
partial pressure-controlled calcination. N atoms next to Cu trigger the CO
2
RR by increasing the amount of CO* on the Cu, lowering the energy needed for CO dimerization.
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.
Perovskite solar cells are promising candidates for realizing an efficient, flexible, and lightweight energy supply system for wearable electronic devices. For flexible perovskite solar cells, ...achieving high power conversion efficiency (PCE) while using a low-temperature technology for the fabrication of a compact charge collection layer is a critical issue. Herein, we report on a flexible perovskite solar cell exhibiting 12.2% PCE as a result of the employment of an annealing-free, 20 nm thick, amorphous, compact TiO sub(x) layer deposited by atomic layer deposition. The excellent performance of the cell was attributed to fast electron transport, verified by time-resolved photoluminescence and impedance studies. The PCE remained the same down to 0.4 sun illumination, as well as to a 45 degree tilt to incident light. Mechanical bending of the devices worsened device performance by only 7% when a bending radius of 1 mm was used. The devices maintained 95% of the initial PCE after 1000 bending cycles for a bending radius of 10 mm. Degradation of the device performance by the bending was the result of crack formation from the transparent conducting oxide layer, demonstrating the potential of the low-temperature-processed TiO sub(x) layer to achieve more efficient and bendable perovskite solar cells, which becomes closer to a practical wearable power source.
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.
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