Wenyu Yuan

The applications of carbon nanotubes and graphene in advanced rechargeable lithium batteries

Advanced rechargeable lithium batteries are desired energy storage devices for electric vehicles. These batteries require their electrodes to have high electrical and thermal conductivity, an appropriate high specific surface area, an outstanding hierarchical architecture, high thermal and chemical stability and to be relatively low cost and environmentally benign. Carbon nanotubes (CNTs) and graphene are two candidate materials that could meet these requirements, and thus have been widely studied. The present paper reviews the applications of CNTs and graphene in batteries, with an emphasis on the particular roles (such as conductive, active, flexible and supporting roles) they play in advanced lithium batteries. We will summarize the unique advantages of CNTs and graphene in battery applications, update the most recent progress, and compare the prospects and challenges of CNTs and graphene for future full utilization in energy storage applications. The effects and mechanisms of heteroatoms doping, the distribution of pore sizes, different architectures (anchored, sandwich-like and wrapped hybrid architecture) are discussed in detail.

Surface engineering-modulated porous N-doped rod-like molybdenum phosphide catalysts: towards high activity and stability for hydrogen evolution reaction over a wide pH range

Electrochemical water splitting is an economic, green and sustainable route to produce hydrogen through the hydrogen evolution reaction (HER). Nowadays, noble metal-free phosphides have been widely used as catalysts in the HER, showing potential applications for both renewable energy production and environmental remediation. Nevertheless, developing surface self-doped MoP electrocatalysts with high HER performances in a wide pH range still remains a challenge. In this work, a novel synthesis strategy was developed to fabricate porous one-dimensional (1D) nitrogen-doped molybdenum phosphide (N-MoP) nanorods. The prepared N-MoP-800 catalyst exhibits a low onset potential of 65 mV and low Tafel slope of 58.66 mV dec−1 in 0.5 M H2SO4, which is almost 2 times higher than that of the pristine MoP nanorod anode. Furthermore, the N-MoP materials show long-term durability for 12 h in a wide pH range. The synergistic effects of pyridinic N and N doping in MoP are responsible for the high catalytic activity of N-MoP under acidic conditions, while the N-Mo component plays a key role in enhancing the HER activity of N-MoP. These interesting findings are helpful for the rational design of highly active HER catalysts. More importantly, this study provides a new strategy to synthesize highly active catalysts with low costs for clean energy conversion.

Highly flexible, foldable and stretchable Ni–Co layered double hydroxide/polyaniline/bacterial cellulose electrodes for high-performance all-solid-state supercapacitors

A novel flexible nickel–cobalt layered double hydroxide/polyaniline/bacterial cellulose (NiCo-LDH/PANI/BC) electrode with both excellent electrochemical and mechanical performances is obtained through successively coating PANI and NiCo-LDH on BC. In addition to making the 3D open network (BC) conductive, the PANI layer also functions as a “nanoglue” to uniformly and robustly immobilize nanostructured NiCo-LDH onto the highly enlarged surface of PANI/BC nanofibers owing to its rough surface and hydrophilicity. Benefitting from the hierarchical structure with a 3D conductive network, unobstructed channels, numerous electroactive sites and induced synergistic effect, the NiCo-LDH/PANI/BC electrode shows excellent electrochemical performance in an aqueous electrolyte, exhibiting a high specific capacitance of 1690 F g−1 (761 C g−1) at 1 A g−1, enhanced rate capability (778 F g−1 or 350 C g−1 at 15 A g−1) and outstanding cycling stability (83.2% capacitance retention after 5000 cycles). Besides, the NiCo-LDH/PANI/BC also shows excellent foldability, high tensile strength (90.8 ± 4.9 MPa), high elongation at break (7.2 ± 0.7%) and outstanding electrochemical stability during bending and stretching. Moreover, a flexible all-solid-state supercapacitor is assembled with NiCo-LDH/PANI/BC as the positive electrode and N-doped carbonized BC/carbon cloth as the negative electrode, delivering a high energy density of 47.3 W h kg−1 at a power density of 828.9 W kg−1, and superior cycling stability (91.4% capacitance retention after 3000 cycles). Therefore, this work provides a new path for high-performance flexible energy storage devices and offers a new vision for uniformly and robustly assembling nanohybrids.

Carbon Nanotubes for Electrochemical Capacitors

Abstract In recent years, much research has been conducted in the application of carbon nanotubes (CNTs) in supercapacitors. Considering that the performance of supercapacitors largely depends more on the electrode architectures than on the intrinsic properties of CNTs, especially in the case of hybrid electrodes whose synergetic effect plays a crucial role, the designing (or controlling) of CNT architectures is thus of great importance. Because architectures with suitable design can provide a highly conductive network with highly accessible specific surface area (SSA) and proper pore size distribution (PSD), which are crucial for charge transportation and ion diffusion, a review focusing more on the electrode architectures is necessary. This chapter focuses particularly on the elaboration of designing and controlling the architecture/structure of CNT-based electrodes, as well as their effects on material properties such as effective SSA and PSD as well as the device performance of electrochemical capacitors (ECs). After a brief introduction of energy storage mechanisms of ECs and the effect of PSD, the development and challenges for the electrode based on CNTs and nanocarbon hybrid architectures are discussed in detail.