WC Nanocrystals Grown on Vertically Aligned Carbon Nanotubes: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction

Single nanocrystalline tungsten carbide (WC) was first synthesized on the tips of vertically aligned carbon nanotubes (VA-CNTs) with a hot filament chemical vapor deposition (HF-CVD) method through the directly reaction of tungsten metal with carbon source. The VA-CNTs with preservation of vertical structure integrity and alignment play an important role to support the nanocrystalline WC growth. With the high crystallinity, small size, and uniform distribution of WC particles on the carbon support, the formed WC–CNTs material exhibited an excellent catalytic activity for hydrogen evolution reaction (HER), giving a η₁₀ (the overpotential for driving a current of 10 mA cm^–2) of 145 mV, onset potential of 15 mV, exchange current density@ 300 mV of 117.6 mV and Tafel slope values of 72 mV dec^–1 in acid solution, and η₁₀ of 137 mV, onset potential of 16 mV, exchange current density@ 300 mV of 33.1 mV and Tafel slope values of 106 mV dec^–1 in alkaline media, respectively. Electrochemical stability test further confirms the long-term operation of the catalyst in both acidic and alkaline media

M₃C (M: Fe, Co, Ni) Nanocrystals Encased in Graphene Nanoribbons: An Active and Stable Bifunctional Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reactions

Transition metal carbide nanocrystalline M₃C (M: Fe, Co, Ni) encapsulated in graphitic shells supported with vertically aligned graphene nanoribbons (VA-GNRs) are synthesized through a hot filament chemical vapor deposition (HF-CVD) method. The process is based on the direct reaction between iron group metals (Fe, Co, Ni) and carbon source, which are facilely get high purity carbide nanocrystals (NCs) and avoid any other impurity at relatively low temperature. The M₃C-GNRs exhibit superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope (39, 41, and 45 mV dec^–1 for Fe₃C-GNRs, Co₃C-GNRs, and Ni₃C-GNRs, respectively), positive onset potential (∼0.8 V), high electron transfer number (∼4), and long-term stability (no obvious drop after 20 000 s test). The M₃C-GNRs catalyst also exhibits remarkable hydrogen evolution reaction (HER) activity with a large cathodic current density of 166.6, 79.6, and 116.4 mA cm^–2 at an overpotential of 200 mV, low onset overpotential of 32, 41, and 35 mV, small Tafel slope of 46, 57, and 54 mV dec^–1 for Fe₃C-GNRs, Co₃C-GNRs, and Ni₃C-GNRs, respectively, as well as an excellent stability in acidic media

Architecture of CuS/PbS Heterojunction Semiconductor Nanowire Arrays for Electrical Switches and Diodes

CuS/PbS p–n heterojunction nanowires arrays have been successfully synthesized. Association of template and DC power sources by controllable electrochemistry processes offers a technique platform to efficiently grow a combined heterojunction nanowire arrays driven by a minimization of interfacial energy. The resulting p–n junction materials of CuS/PbS show highly uniform 1D wire architecture. The single CuS/PbS p–n heterojunction nanowire based devices were fabricated, and their electrical behaviors were investigated. The independent nanowires exhibited a very high ON/OFF ratio of 1195, due to the association effect of electrical switches and diodes

Highly Efficient Hydrogen Evolution from Edge-Oriented WS_{2(1–<i>x</i>)}Se_2<i>x</i> Particles on Three-Dimensional Porous NiSe₂ Foam

The large consumption of natural fossil fuels and accompanying environmental problems are driving the exploration of cost-effective and robust catalysts for hydrogen evolution reaction (HER) in water splitting. Tungsten dichalcogenides (WS₂, WSe₂, etc.) are promising candidates for such purpose, but their HER performances are inherently limited by the sparse catalytic edge sites and poor electrical conductivity. Here we demonstrate a highly active and stable HER catalyst by integrating ternary tungsten sulfoselenide WS_{2(1–<i>x</i>)}Se_2<i>x</i> particles with a 3D porous metallic NiSe₂ foam, in which good electrical conductivity, good contact, large surface area, and high-density active edge sites are simultaneously obtained, thus contributing to outstanding catalytic performance: large cathode current density (−10 mA/cm² at −88 mV), low Tafel slope (46.7 mV/dec), large exchange current density (214.7 μA/cm²), and good stability, which is better than most reports on WS₂ and NiSe₂ catalysts. This work paves an interesting route for boosting HER efficiency of transition metal dichalcogenide catalysts

Engineering Multilevel Collaborative Catalytic Interfaces with Multifunctional Iron Sites Enabling High-Performance Real Seawater Splitting

Given the abundant reserves of seawater and the scarcity of freshwater, real seawater electrolysis is a more economically appealing technology for hydrogen production relative to orthodox freshwater electrolysis. However, this technology is greatly precluded by the undesirable chlorine oxidation reaction and severe chloride corrosion at the anode, further restricting the catalytic efficiency of overall seawater splitting. Herein, a feasible strategy by engineering multifunctional collaborative catalytic interfaces is reported to develop porous metal nitride/phosphide heterostructure arrays anchoring on conductive Ni2P surfaces with affluent iron sites. Collaborative catalytic interfaces among iron phosphide, bimetallic nitride, and porous Ni2P supports play a positive role in improving water adsorption/dissociation and hydrogen adsorption behaviors of active Fe sites evidenced by theoretical calculations for hydrogen evolution reactions, and enhancing oxygenated species adsorption and nitrate-rich passivating layers resistant to chloride corrosion for oxygen evolution reaction, thus cooperatively propelling high-performance bifunctional seawater splitting. The resultant material Fe2P/Ni1.5Co1.5N/Ni2P performs excellently as a self-standing bifunctional catalyst for alkaline seawater splitting. It requires extremely low cell voltages of 1.624 and 1.742 V to afford current densities of 100 and 500 mA/cm2 in 1 M KOH seawater electrolytes, respectively, along with superior long-term stability, outperforming nearly all the ever-reported non-noble bifunctional electrocatalysts and benchmark Pt/IrO2 coupled electrodes for freshwater/seawater electrolysis. This work presents an effective strategy for greatly enhancing the catalytic efficiency of non-noble catalysts toward green hydrogen production from seawater electrolysis

Three-Dimensional Nanoporous Iron Nitride Film as an Efficient Electrocatalyst for Water Oxidation

Exploring efficient and durable catalysts from earth-abundant and cost-effective materials is highly desirable for the sluggish anodic oxygen evolution reaction (OER), which plays a key role in water splitting, fuel cells, and rechargeable metal–air batteries. First-row transition-metal (Ni, Co, and Fe)-based compounds are promising candidates as OER catalysts to substitute the benchmark of noble-metal-based catalysts, such as IrO₂ and RuO₂. Although Fe is the cheapest and one of the most abundant transition-metal elements, there are seldom papers reported on Fe-only compounds with outstanding catalytic OER activities. Here we propose an interesting strategy by growing iron nitride (Fe₃N/Fe₄N) based nanoporous film on three-dimensional (3D) highly conductive graphene/Ni foam, which is demonstrated to be a robust and durable self-supported 3D electrode for the OER featuring a very low overpotential of 238 mV to achieve a current density of 10 mA/cm², a small Tafel slope of 44.5 mV/dec, good stability, and 96.7% Faradaic yield. The high OER efficiency is by far one of the best for single-metal (Fe, Co, and Ni)-based catalysts, and even better than that of the benchmark IrO₂, which is attributed to the fast electron transfer, high surface area, and abundant active sites of the catalyst. This development introduces another member to the family of cost-effective and efficient OER catalysts

Atomic H‑Induced Mo₂C Hybrid as an Active and Stable Bifunctional Electrocatalyst

Mo₂C nanocrystals (NCs) anchored on vertically aligned graphene nanoribbons (VA-GNR) as hybrid nanoelectrocatalysts (Mo₂C–GNR) are synthesized through the direct carbonization of metallic Mo with atomic H treatment. The growth mechanism of Mo₂C NCs with atomic H treatment is discussed. The Mo₂C–GNR hybrid exhibits highly active and durable electrocatalytic performance for the hydrogen-evolution reaction (HER) and oxygen-reduction reaction (ORR). For HER, in an acidic solution the Mo₂C–GNR has an onset potential of 39 mV and a Tafel slope of 65 mV dec^–1, and in a basic solution Mo₂C–GNR has an onset potential of 53 mV, and Tafel slope of 54 mV dec^–1. It is stable in both acidic and basic media. Mo₂C–GNR is a high-activity ORR catalyst with a high peak current density of 2.01 mA cm^–2, an onset potential of 0.93 V that is more positive vs reversible hydrogen electrode (RHE), a high electron transfer number <i>n</i> (∼3.90), and long-term stability

Hexagonal Graphene Onion Rings

Precise spatial control of materials is the key capability of engineering their optical, electronic, and mechanical properties. However, growth of graphene on Cu was revealed to be seed-induced two-dimensional (2D) growth, limiting the synthesis of complex graphene spatial structures. In this research, we report the growth of onion ring like three-dimensional (3D) graphene structures, which are comprised of concentric one-dimensional hexagonal graphene ribbon rings grown under 2D single-crystal monolayer graphene domains. The ring formation arises from the hydrogenation-induced edge nucleation and 3D growth of a new graphene layer on the edge and under the previous one, as supported by first principles calculations. This work reveals a new graphene-nucleation mechanism and could also offer impetus for the design of new 3D spatial structures of graphene or other 2D layered materials. Additionally, in this research, two special features of this new 3D graphene structure were demonstrated, including nanoribbon fabrication and potential use in lithium storage upon scaling