A bis-diketopyrrolopyrrole (DPP dimer, 2DPP) core is synthesized with much stronger electron deficiency than DPP by homocoupling of DPP. 2DPP-based polymers, P2DPP-BT, P2DPP-TT, P2DPP-TVT, and P2DPP-BDT, are obtained. Top-gated organic field-effect transistors on plastic substrate are fabricated. Compared with their mono-DPP-based polymers, remarkable improvement of electron mobilities of P2DPPs is achieved. Meanwhile, their p-channel performance becomes higher.

So far, most of the reported high-mobility conjugated polymers are p-type semiconductors. By contrast, the advances in high-mobility ambipolar polymers fall greatly behind those of p-type counterparts. Instead of unipolar p-type and n-type materials, ambipolar polymers, especially balanced ambipolar polymers, are potentially serviceable for easy-fabrication and low-cost complementary metal-oxide-semiconductor circuits. Therefore, it is a critical issue to develop high-mobility ambipolar polymers. Here, three isoindigo-based polymers, PIID-2FBT, P1FIID-2FBT, and P2FIID-2FBT are developed for high-performance ambipolar organic field-effect transistors. After the incorporation of fluorine atoms, the polymers exhibit enhanced coplanarity, lower energy levels, higher crystallinity, and thus increased µe. P2FIID-2FBT exhibits n-type dominant performance with a µe of 9.70 cm2 V−1 s−1. Moreover, P1FIID-2FBT exhibits a highly balanced µh and µe of 6.41 and 6.76 cm2 V−1 s−1, respectively, which are among the highest values for balanced ambipolar polymers. Moreover, a concept “effective mass” is introduced to further study the reasons for the high performance of the polymers. All the polymers have small effective masses, indicating good intramolecular charge transport. The results demonstrate that high-mobility ambipolar semiconductors can be obtained by designing polymers with fine-tuned energy levels, small effective masses, and high crystallinity.

Flexible, wearable, implantable and easily reconfigurable micro-fabricated pseudocapacitors with impressive volumetric stack capacitance and energy densities are desired for electronic devices. In this work, scratching technology at the micron-scale enables construction of the planar electrode systems directly based on nanoporous gold films. We demonstrate that both nanoporous channels with high ion-accessible ability and interconnected skeletons with high conductivity enable the design of pseudocapacitive micro-supercapacitors with high performances. These planar devices show several attractive features including ultrafast charge/discharge (high rate), large capacitance (1.27 mF cm−2, 127 F cm−3), and ultrahigh energy density (0.045 W h cm−3) while maintaining a high power density (22.21 W cm−3). Especially, the superb cyclability and mechanical flexibility give them great potential for future microelectronics with a tiny volume. The design concept reported here provides an avenue to integrate planar micro-supercapacitors into large-scale devices with a small environmental footprint.

•A facile approach is proposed to synthesize ultra-small Fe2N nanocrystals/MNGCS.•The Fe2N content and BET surface area of Fe2N/MNGCS can be adjusted by altering the acid etching time.•The optimized Fe2N/MNGCS catalyst demonstrates better ORR performance than 10 wt% Pt/C catalyst.•Such excellent performance is ascribed to the rational balance of the density of Fe–N/C active sites, and the transport of electron and electrolyte ion.A low-cost, highly active, stable, and methanol tolerant electrocatalyst towards the oxygen reduction reaction (ORR) is extremely desirable for promoting the commercialization of fuel cells. Herein, we reported a facile two-step pyrolysis and acid leaching process to synthesize a high performance ORR electrocatalyst, where ultra-small Fe2N nanocrystals were incorporated into mesoporous nitrogen-doped graphitic carbon spheres (MNGCS). The Fe2N/MNGCS electrocatalysts with difference Fe2N contents and BET surface areas were obtained via altering the acid leaching time, and all exhibited the apparent electrocatalytic activity. The optimized ORR activity was achieved over (Fe2N/MNGCS)4 with the positive half-wave potentials (0.881 V vs RHE), high selectivity (4 e− process), excellent long-term stability (95.2% of the initial current remaining after 60,000 s of continuous operation) and good tolerance against methanol-crossover effect (94.9% of the current retained prior to 4.0 M methanol injection) in alkaline media, which even was more superior to that of commercial Pt/C catalyst. The remarkable ORR activity was originated from the cooperative effect of ultra-small Fe2N nanocrystals and MNGCS, where the balance of catalytic active site density, mesoporous structure, BET specific surface area, and electron conductivity played a key role in determining the ORR performance.

Balanced carrier transport is observed in acceptor-acceptor (A-A′) type polymer for ambipolar organic thin-film transistors (OTFTs). It is found that the incorporation of two electron-accepting moieties (BTz and IIG) into a polymer main chain to form A-A′ polymer PIIG-BTz could lower highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and facilitate good molecular stacking of the polymer. Ambipolar transistor behaviour for PIIG-BTz, with the balanced hole and electron mobilities of 0.030 and 0.022 cm2 V−1 s−1 was observed in OTFT devices, respectively. The study in this work reveals that the utilization of acceptor-acceptor (A-A′) structure in polymer main chain can be a feasible strategy to develop ambipolar polymer semiconductors.

Although the NiO nanostructures potentially hold outstanding electrochemical activity in theory, dual enhancements in both electrical conductivity and electrolyte transport are two challenging issues for designing high performance electrodes. In this work, hierarchical porous Ni/NiO core–shells are synthesized. The interconnected Ni skeletons with favorable electrical conductivity are uniformly covered by the continuous NiO scarfskins that hold both high energy storage capacity and efficient catalysis. The hierarchical porous Ni/NiO electrode exhibits superior pseudo-capacitive performance evidenced by an areal capacitance up to 255 mF cm−2. Meanwhile, this conductive electrode also exhibits electrocatalytic activity for glucose oxidation with a sensitivity of 4.49 mA mM−1 cm−2 and a reliable detection limit of 10 μM. On the other hand, hierarchical porosities enhance the effective transport of electrolytes and ions within the interconnected porous channels, making dramatic contributions to a superior storage stability of 4000 cycles and prompt an amperometric response time of 1.5 s. These concepts of the hierarchical metal–metal oxide core–shell open an avenue to design high-performance materials for energy storage and electrochemical catalysis.

A facile approach is reported to synthesize (Fe,Co)@nitrogen-doped graphitic carbon (NGC) nanocubes (NCs) via the pyrolysis of polydopamine-encapsulated Fe3[Co(CN)6]2 NCs at 700 °C. Besides the comparable catalytic activity for oxygen reduction reaction (ORR) to the Pt/C catalyst, it showed much more outstanding catalytic selectivity and superior durability.

Gold nanoparticles with nanoscale protrusions can be synthesized by seed-mediated growth in favor of tuning the surface plasmon band towards the near-infrared regime. Electromagnetic field enhancement makes significant contribution to improve fluorescence emission of PbS quantum dots in the near-infrared window, identifying their application in remote imaging by collecting the scattered fluorescence of their hybrids.

We developed a synthetic strategy for enhancing organic thin-film transistor performances of polymer semiconductors through the modification of the side chain to optimize the stacking conformation and the conjugated backbone to decrease the π–π stacking distance of polymers. Our studies demonstrate that the role of bulky alkyl chains attached to the donor unit or the acceptor unit is especially crucial for molecular stacking and aggregation and thus the OTFT device performance of polymers. However, with a larger π–π stacking distance in the thin film, the polymer with a bulky alkyl chain attached at the acceptor (P2) shows almost two orders of magnitude higher mobility than that with a bulky alkyl chain attached at the donor (P1). The better performance for P2 is attributed to the bulky alkyl chain at the acceptor which allows more coplanarity of the P2 backbone in the solution state, which leads to self-assembly, and finally forms a highly ordered layer-by-layer lamellar packing for P2 during spin-coating. Further improved performances were obtained by introducing two thiophene units into the polymer backbone to give P3, due to closer π–π stacking and in-plane π-stacking alignment in the thin film and a higher HOMO energy level. Therefore, an optimized device performance was realized through subtle modification of the polymer structure, including both the main chain and the side chain, which provides an insight into structure–property relationships for high-mobility polymer semiconductors.

•MOx nanorod arrays are grown on the carbon fiber papers via a hydrothermal method.•GNR and GNS are deposited on the MOx nanorods via a facile dipping-coating method.•The electrochemical performance is enhanced with the introduction of GNR and GNS.•A high performance (MOx/GNR)@GNS-based solid-stated cells is successfully achieved.Electrochemical capacitors and rechargeable batteries are still limited in applications by the low energy and power densities they can deliver, respectively, holding back their deployment in electric vehicles. Here we develop a type of solid-state hybrid cells (SHCs) composed of graphene nanoribbons and nanosheets-coated metal oxide nanorod arrays ((MOx/GNR)@GNS). GNR and GNS are deposited on the surface of MOx nanorod arrays to improve the electron transport characteristic, and thus enhance the energy storage performance. The (MOx/GNR)@GNS-based SHCs can achieve a maximum volumetric energy density of 0.9 mWh cm−3, and still retain 0.4 mWh cm−3 even at 0.1 W cm−3. The energy storage performance is much better than the electrochemical capacitors reported previously, and can even rival the commercial Li thin-film battery but with a significantly higher power density, lower cost and higher safety. Also demonstrated is the good long-term cycle life with only ∼17% loss after 2500 cycles. These salient features make the (MOx/GNR)@GNS composites-based SHCs a strong contender for electrochemical energy storage.

Grains and grain boundaries (GBs) in graphene are vital for the control of its properties; however, engineering or controlling them by growth remains a great challenge. Here we discover that the dynamic formation of GBs within chemical vapor deposited polygonal graphene flakes is described by a geometric rule. A GB is formed to be symmetrically tilted and a continuous straight line, and the key parameters including end point, direction of GB line, and misorientation angles between adjacent graphene grains can be determined solely by the geometries of the polygonal graphene flakes. We also show the growth control over the length of straight graphene GB lines and demonstrate the capability of parallel fabrication of field-effect transistor devices across predicted GBs in a straightforward manner. This work constitutes a significant step forward in engineering grains and GBs in graphene.Keywords: anisotropic etching; chemical vapor deposition; dynamic formation; grain boundaries; graphene;

The relatively poor dynamic response of current flexible strain gauges has prevented their wide adoption in portable electronics. In this work, we present a greatly improved flexible strain gauge, where one strip of Au nanoparticle (NP) monolayer assembled on a polyethylene terephthalate film is utilized as the active unit. The proposed flexible gauge is capable of responding to applied stimuli without detectable hysteresis via electron tunneling between adjacent nanoparticles within the Au NP monolayer. Based on experimental quantification of the time and frequency domain dependence of the electrical resistance of the proposed strain gauge, acoustic vibrations in the frequency range of 1 to 20,000 Hz could be reliably detected. In addition to being used to measure musical tone, audible speech, and creature vocalization, as demonstrated in this study, the ultrafast dynamic response of this flexible strain gauge can be used in a wide range of applications, including miniaturized vibratory sensors, safe entrance guard management systems, and ultrasensitive pressure sensors.

The controllable synthesis of transition metal oxide nanomaterials has attracted considerable attention for the replacement of the current precious metal catalysts. Herein, we have developed a facile method to successfully synthesize Mn3O4–CoO core–shell mesoporous spheres, which are wrapped by carbon nanotubes (CNT), and investigated the catalytic activity for the oxygen reduction reaction (ORR) and CO oxidation for the first time. The ORR process on the Mn3O4–CoO/CNT catalysts was via a complete oxygen reduction process (4e−), and the catalytic activity was far better than for the Mn3O4/CNT and CoO/CNT catalysts. The durability even out-performed the commercial Pt/C catalysts. As compared with the Mn3O4/CNT and CoO/CNT catalysts, the Mn3O4–CoO/CNT catalysts also exhibited better catalytic activity for CO oxidation. The initial and complete conversion temperatures for the Mn3O4–CoO/CNT catalysts can decrease to 30 and 120 °C, respectively. The good catalytic activity for the ORR and CO oxidation is due to the high specific surface area (138.9 m2 g−1) provided which gives many catalytically active sites, mesoporous structure (15 to 120 nm) favoured for molecule accessibility to the active surface of the nanocrystals and mass transport, and the synergistic catalytic effect of Mn3O4 and CoO catalytically active sites.

The electrochemical performance of the pseudocapacitive materials is seriously limited by poor electron and ions transport. Herein, an advanced integrated electrode has been designed by growing the pseudocapacitive materials, including CoxNi1–x(OH)2, CoxNi1–xO, and (CoxNi1–x)9S8, on a three-dimensional hollow carbon nanorod arrays (HCNA) scaffold. The HCNA scaffold not only can provide large surface area for increasing the mass loading of the pseudocapacitive materials, but also is with good electrical conductivity and hollow structure for facilitating fast electron and electrolyte ions transport, and thus improve the electrochemical performance. Particularly, in comparison with CoxNi1–x(OH)2 and CoxNi1–xO nanosheets, (CoxNi1–x)9S8 nanosheets on the HCNA scaffold exhibit better electrochemical performance. The discharge areal capacitance of the (CoxNi1–x)9S8/HCNA electrode can be achieved to 1.32 F cm–2 at 1 mA cm–2, ∼1.5 times as that of the CoxNi1–x(OH)2/HCNA electrode. The rate capability performance is also improved. 71.8% of the capacitance is retained with increasing the discharge current density from 1 to 10 mA cm–2, in contrast to ∼59.9% for the CoxNi1–x(OH)2/HCNA electrode. Remarkably, the cycling stability is significantly enhanced. ∼111.2% of the initial capacitance is gained instead of decaying after the 3000 cycles at 8 mA cm–2, while there is ∼11.5% loss for the CoxNi1–x(OH)2/HCNA electrode tested under the same condition. Such good electrochemical performance can be ascribed by that (CoxNi1–x)9S8 exhibits the similar energy storage mechanism as CoxNi1–x(OH)2 and CoxNi1–xO, and more importantly, is with better electrical conductivity.Keywords: (Co, Ni)-based compounds; carbon fiber paper; hollow carbon nanorod array; supercapacitors; three-dimensional; ZnO nanorod array;

The reliability and sensitivity of a strain gauge made from a nanoparticle monolayer intrinsically depend on electron tunneling between the adjacent nanoparticles, so that creating nanoscale interstitials with uniform distribution and tuning the interparticle separation reversibly during cyclic mechanical stress are two vital issues for performance enhancement. In this work, one assembly technique is initialized to fabricate parallel nanoparticle strips by precisely tailoring the contact angle of a gold colloid on a substrate. The assembly of a nanoparticle monolayer with a close-packed pattern can be simultaneously switched on and off by independently varying the contact angle across a threshold value of 4.2°. This nanoparticle strip shows a reversible and reliable electrical response even if a mechanical strain as small as 0.027% is periodically supplied, implying well-controlled electron tunneling between the adjacent nanoparticles.

Self-standing single crystalline NiCo2S4 hollow nanorod arrays are prepared for catalysing the polysulfide redox couple in quantum dot-sensitized solar cells (QDSCs). The QDSCs using NiCo2S4 as a counter electrode (CE) achieved a power conversion efficiency of 4.22%, which exceeds the performance of QDSCs based on a Pt CE by 38.4%.

Transition metal oxides with hierarchically porous structures supported by conductive substrates have been considered as promising electrodes for electrochemical energy storage and catalysis. Herein we configure porous Co3O4/C nanowire arrays (NAs) by thermally annealing a Co-based metal–organic framework (Co-MOF) in Ar and air, respectively. The hybrid Co3O4/C NAs demonstrate a high specific capacitance of 1.32 F cm−2 at a current density of 1 mA cm−2, which is much superior to that of bare Co3O4 NAs. A highly stable symmetric supercapacitor based on Co3O4/C exhibits an excellent durability with only 21.7% capacitance decay after 5000 cycles. Besides electrochemical energy storage, the Co3O4/C hybrids demonstrate an outstanding electrochemical catalysis ability for the oxygen evolution reaction, identified by the high current density of 30 mA cm−2 at low overpotential (η30 = 318 mV) and a small Tafel slope (81 mV dec−1). The electrical conductivity of the interconnected C infrastructures and ion diffusion within the hierarchical pores are intrinsic causes to promote the pseudo-capacitive performance and enhance catalytic activity. The synthesis strategy reported here opens an avenue to design high performance electrodes for energy storage and electrochemical catalysis.

Self-standing single crystalline NiCo2S4 hollow nanorod arrays are prepared for catalysing the polysulfide redox couple in quantum dot-sensitized solar cells (QDSCs). The QDSCs using NiCo2S4 as a counter electrode (CE) achieved a power conversion efficiency of 4.22%, which exceeds the performance of QDSCs based on a Pt CE by 38.4%.

The controllable synthesis of transition metal oxide nanomaterials has attracted considerable attention for the replacement of the current precious metal catalysts. Herein, we have developed a facile method to successfully synthesize Mn3O4–CoO core–shell mesoporous spheres, which are wrapped by carbon nanotubes (CNT), and investigated the catalytic activity for the oxygen reduction reaction (ORR) and CO oxidation for the first time. The ORR process on the Mn3O4–CoO/CNT catalysts was via a complete oxygen reduction process (4e−), and the catalytic activity was far better than for the Mn3O4/CNT and CoO/CNT catalysts. The durability even out-performed the commercial Pt/C catalysts. As compared with the Mn3O4/CNT and CoO/CNT catalysts, the Mn3O4–CoO/CNT catalysts also exhibited better catalytic activity for CO oxidation. The initial and complete conversion temperatures for the Mn3O4–CoO/CNT catalysts can decrease to 30 and 120 °C, respectively. The good catalytic activity for the ORR and CO oxidation is due to the high specific surface area (138.9 m2 g−1) provided which gives many catalytically active sites, mesoporous structure (15 to 120 nm) favoured for molecule accessibility to the active surface of the nanocrystals and mass transport, and the synergistic catalytic effect of Mn3O4 and CoO catalytically active sites.

Flexible, wearable, implantable and easily reconfigurable micro-fabricated pseudocapacitors with impressive volumetric stack capacitance and energy densities are desired for electronic devices. In this work, scratching technology at the micron-scale enables construction of the planar electrode systems directly based on nanoporous gold films. We demonstrate that both nanoporous channels with high ion-accessible ability and interconnected skeletons with high conductivity enable the design of pseudocapacitive micro-supercapacitors with high performances. These planar devices show several attractive features including ultrafast charge/discharge (high rate), large capacitance (1.27 mF cm−2, 127 F cm−3), and ultrahigh energy density (0.045 W h cm−3) while maintaining a high power density (22.21 W cm−3). Especially, the superb cyclability and mechanical flexibility give them great potential for future microelectronics with a tiny volume. The design concept reported here provides an avenue to integrate planar micro-supercapacitors into large-scale devices with a small environmental footprint.

A facile approach is reported to synthesize (Fe,Co)@nitrogen-doped graphitic carbon (NGC) nanocubes (NCs) via the pyrolysis of polydopamine-encapsulated Fe3[Co(CN)6]2 NCs at 700 °C. Besides the comparable catalytic activity for oxygen reduction reaction (ORR) to the Pt/C catalyst, it showed much more outstanding catalytic selectivity and superior durability.

Gold nanoparticles with nanoscale protrusions can be synthesized by seed-mediated growth in favor of tuning the surface plasmon band towards the near-infrared regime. Electromagnetic field enhancement makes significant contribution to improve fluorescence emission of PbS quantum dots in the near-infrared window, identifying their application in remote imaging by collecting the scattered fluorescence of their hybrids.

Although the NiO nanostructures potentially hold outstanding electrochemical activity in theory, dual enhancements in both electrical conductivity and electrolyte transport are two challenging issues for designing high performance electrodes. In this work, hierarchical porous Ni/NiO core–shells are synthesized. The interconnected Ni skeletons with favorable electrical conductivity are uniformly covered by the continuous NiO scarfskins that hold both high energy storage capacity and efficient catalysis. The hierarchical porous Ni/NiO electrode exhibits superior pseudo-capacitive performance evidenced by an areal capacitance up to 255 mF cm−2. Meanwhile, this conductive electrode also exhibits electrocatalytic activity for glucose oxidation with a sensitivity of 4.49 mA mM−1 cm−2 and a reliable detection limit of 10 μM. On the other hand, hierarchical porosities enhance the effective transport of electrolytes and ions within the interconnected porous channels, making dramatic contributions to a superior storage stability of 4000 cycles and prompt an amperometric response time of 1.5 s. These concepts of the hierarchical metal–metal oxide core–shell open an avenue to design high-performance materials for energy storage and electrochemical catalysis.