Graphene sheets wrapped carbon nanofibers as a highly conductive three-dimensional framework for perpendicularly anchoring of MoS 2 : Advanced electrocatalysts for hydrogen evolution reaction

Introducing phosphorus atoms into MoS2 nanosheets through a vapor-phase hydrothermal process for the hydrogen evolution reaction

Molybdenum disulfide (MoS2)-based electrocatalysts have been considered as promising alternatives to platinum for use in the hydrogen evolution reaction (HER). Developing MoS2 electrocatalysts with more active sites has been recognized as an efficient way to enhance the HER activity. Moreover, phase transition and heteroatom doping show great influence on the HER performance. In this work, we develop a vapor-phase hydrothermal (VPH) approach to introduce phosphorus (P) atoms into a MoS2 nanosheet array on carbon fiber cloth, which presents enhanced HER activity compared with MoS2 without P-doping. The improved performance is due to the synergistic effects of the new active sites formed by the P dopants and the sulfur (S) vacancies in the MoS2 nanosheets generated by the doping of P atoms, which increases the number of active sites. In general, the obtained P-doped MoS2/CFC exhibits a lower onset potential of 80 mV and an overpotential of 162 mV at 10 mA cm-2 than MoS2 without P-doping in 0.5 M H2SO4, accompanied by extremely large cathodic current density and excellent stability. This strategy may open up opportunities for heteroatom doping of electrocatalysts for various applications and provide a new method for material synthesis.

Amorphous materials for elementary-gas-involved electrocatalysis: an overview

Given the critical demands on energy conversion, storage, and transportation, tremendous interest has been devoted to the field of material development related to energy harvesting, recently. As the only route towards energy utilization, the carriers with the characteristics of low carbon are regarded as the future choice, e.g., hydrogen and ammonia. To this end, electrocatalysis provides a green way to access these substances. However, the unfulfilled conversion efficiency is the bottleneck for practical application. In this review, the promising characteristics of amorphous materials and the amorphous-induced electrocatalytic enhancement (AIEE) were emphasized. In the beginning, the characteristics of amorphous materials are briefly summarized. The basic mechanism of heterogeneous electrocatalytic reactions is illustrated, including the hydrogen/oxygen evolution and oxygen/nitrogen reduction. In the third part, the electrocatalytic performance of amorphous materials is discussed in detail, and the mechanism of AIEE is highlighted. In the last section of this review, the challenges and outlook for the development of amorphous enhanced electrocatalysis are presented.

Graphene Nanoarchitectonics: Recent Advances in Graphene-Based Electrocatalysts for Hydrogen Evolution Reaction

Under the double pressures of both the energy crisis and environmental pollution, the exploitation and utilization of hydrogen, a clean and renewable power resource, has become an important trend in the development of sustainable energy-production and energy-consumption systems. In this regard, the electrocatalytic hydrogen evolution reaction (HER) provides an efficient and clean pathway for the mass production of hydrogen fuel and has motivated the design and construction of highly active HER electrocatalysts of an acceptable cost. In particular, graphene-based electrocatalysts commonly exhibit an enhanced HER performance owing to their distinctive structural merits, including a large surface area, high electrical conductivity, and good chemical stability. Considering the rapidly growing research enthusiasm for this topic over the last several years, herein, a panoramic review of recent advances in graphene-based electrocatalysts is presented, covering various advanced synthetic strategies, microstructural characterizations, and the applications of such materials in HER electrocatalysis. Lastly, future perspectives on the challenges and opportunities awaiting this emerging field are proposed and discussed.

Facile synthesis of reduced graphene oxide-wrapped CNFs with controllable chemical reduction degree for enhanced microwave absorption performance

The rGO-wrapped nanocomposites can be regarded as promising candidates for the development of advanced microwave absorbing materials. In this work, hierarchical rGO-wrapped CNFs were prepared via a two-step strategy, including a classical modified Hummers method and a green reduction reaction. Accompany with the chemical treatments, graphene oxide appears on the outer walls of carbon nanofibers. By modulating the addition amount of ascorbic acid, the outer graphene oxide can be controllably reduced. Moreover, the CNFs/rGO with proper reduction degree exhibits desirable microwave absorption performance, whose minimum RL and effective bandwidth are -38.1 dB (3.85 GHz, d = 5.0 mm) and 4.1 GHz (5.08-9.18 GHz, d = 3.5 mm). The superior microwave attenuation performance is attributed to the synergistic effects between the CNFs and rGO. While the nanofibers provide the obtained sample with an extremely long conductive network, rGO introduces a moderate amount of lattice defects and functional groups, resulting in desirable conductivity loss and multiple polarizations. The existence of rGO also endows CNFs/rGO with suitable dielectric values so that the absorber achieves well impedance matching. Considering the excellent microwave absorption performance, this research provides a new facile route to fabricate rGO-wrapped carbonaceous materials with proper oxygen-containing groups for MAMs.

Advanced electrospun nanomaterials for highly efficient electrocatalysis

We highlight the recent developments of electrospun nanomaterials with controlled morphology, composition and architecture for highly efficient electrocatalysis.

C60-Decorated nickel-cobalt phosphide as an efficient and robust electrocatalyst for hydrogen evolution reaction

High-activity electrocatalysts play a crucial role in energy conversion through splitting water to produce hydrogen. Here we report the synthesis of a bimetallic phosphide of Ni-Co-P coupled with C60 molecules which acts as an electrocatalyst for the hydrogen evolution reaction (HER). Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization reveals that the synthesized C60-decorated Ni-Co-P nanoparticles have an average diameter of ∼4 nm with rich structural defects. Electrochemical tests show that the as-synthesized C60-decorated Ni-Co-P catalyst with a C60-content of 3.93 wt% presents a low onset overpotential of 23.8 mV, a small Tafel slope value of 48 mV dec-1, and excellent hydrogen-evolution stability with a slight increase of its η10 from 97 mV to 102 mV after 500 cycles. Additionally, electrochemical impedance spectroscopy (EIS) confirms that the C60-decorated Ni-Co-P electrode possesses faster charge-transfer kinetics and hydrogen-adsorption kinetics than the C60-free Ni-Co-P electrode during the HER process. The synthesis of a C60-decorated composite is feasible and the composite can be used as an efficient and robust Pt-free catalyst.

Phosphorus-doped NiCo2S4 nanocrystals grown on electrospun carbon nanofibers as ultra-efficient electrocatalysts for the hydrogen evolution reaction

The development of highly efficient noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is still a challenge nowadays. In this work, we prepared a highly active electrocatalyst containing phosphorus-doped NiCo₂S₄ nanocrystals grown on carbon nanotube embedded carbon nanofibers (P-NiCo₂S₄@CNT/CNF). The CNTs are involved in enhancing the electrical conductivity of the three-dimensional CNF network through a facile co-electrospinning method, which can facilitate electron transfer to the attached HER active material. Templated by this nanofiber network, the electroactive NiCo₂S₄ is confined to grow perpendicularly onto the CNT/CNF template via a hydrothermal reaction, thus exposing more catalytic active sites. Doping of P into the hybrid via a phosphidation reaction improves the electronic structure of the electroactive NiCo₂S₄, thus decreasing the energy barrier during the HER process. Owing to the synergistic effects from electrical enhancement and the nanostructured morphology, along with P-doping-induced optimization of the electronic structure, the P-NiCo₂S₄@CNT/CNF hybrid exhibits excellent HER performance, with an ultra-low onset overpotential (η) of 27 mV, a remarkable current density of 10 mA cm^-2 at η as low as 74 mV, an impressive exchange current density of 0.79 mA cm^-2 and excellent long-term durability. Furthermore, its electroactivity exceeds that of most reported noble-metal-free electrocatalysts and is comparable to that of Pt, suggesting its great potential as a highly efficient HER catalyst.