Constructing N-Containing Poly(p-Phenylene) (PPP) Films Through A Cathodic-Dehalogenation Polymerization Method

Developing the films of N-containing unsubstituted poly(p-phenylene) (PPP) films for diverse applications is significant and highly desirable because the replacement of sp2 C atoms with sp2 N atoms will bring novel properties to the as-prepared polymers. In this research, an electrochemical-dehalogenation polymerization strategy is employed to construct two N-containing PPP films under constant potentials, where 2,5-diiodopyridine (DIPy) and 2,5-dibromopyrazine (DBPz) are used as starting agents. The corresponding polymers are named CityU-23 (for polypyridine) and CityU-24 (for polypyrazine). Moreover, it is found that both polymers can form films in situ on different conductive substrates (i.e., silicon, gold, ITO, and nickel), satisfying potential device fabrication. Furthermore, the as-obtained thin films of CityU-23 and CityU-24 exhibit good performance of alkaline hydrogen evolution reaction with the overpotential of 212.8 and 180.7 mV and the Tafel slope of 157.0 and 122.4 mV dec-1, respectively.

Electronic Modulation Induced by Ni-VN Heterojunction Reinforces Electrolytic Hydrogen Evolution Coupled with Biomass Upgrade

The renewable electricity-driven hydrogen evolution reaction (HER) coupled with biomass oxidation is a powerful avenue to maximize the energy efficiency and economic feedback, but challenging. Herein, porous Ni-VN heterojunction nanosheets on nickel foam (Ni-VN/NF) are constructed as a robust electrocatalyst to simultaneously catalyze HER and 5-hydroxymethylfurfural electrooxidation reaction (HMF EOR). Benefiting from the surface reconstruction of Ni-VN heterojunction during the oxidation process, the derived NiOOH-VN/NF energetically catalyzes HMF into 2,5-furandicarboxylic acid (FDCA), yielding the high HMF conversion (>99%), FDCA yield (99%), and Faradaic efficiency (>98%) at the lower oxidation potential along with the superior cycling stability. Ni-VN/NF is also surperactive for HER, exhibiting an onset potential of ≈0 mV and Tafel slope of 45 mV dec-1 . The integrated Ni-VN/NF||Ni-VN/NF configuration delivers a compelling cell voltage of 1.426 V at 10 mA cm-2 for the H2 O-HMF paired electrolysis, about 100 mV lower than that for water splitting. Theoretically, for Ni-VN/NF, the superiority in HMF EOR and HER is mainly dominated by the local electronic distribution at the heterogenous interface, which accelerates the charge transfer and optimize the adsorption of reactants/intermediates by modulating the d-band center, therefore being an advisable thermodynamic and kinetic process.

Triggering Pt Active Sites in Basal Plane of Van der Waals PtTe2 Materials by Amorphization Engineering for Hydrogen Evolution

Exposing active sites and optimizing their bonding strength to reaction intermediates are two essential strategies to significantly improve the catalytic performance of two-dimensional (2D) materials. However, pursuing an efficient way to achieve these goals simultaneously remains a considerable challenge. Here, using 2D PtTe₂ van der Waals material with well-defined crystal structure and atomically thin thickness as a model catalyst, we observe that a moderate calcination strategy can promote the structural transformation of 2D crystal PtTe₂ nanosheets (c-PtTe₂ NSs) into oxygen-doped 2D amorphous PtTe₂ NSs (a-PtTe₂ NSs). The experimental and theoretical investigations cooperatively reveal that oxygen dopants can break the inherent Pt-Te covalent bond in c-PtTe₂ NSs, thereby triggering the reconfiguration of interlayer Pt atoms and exposing them thoroughly. Meanwhile, the structural transformation can effectively tailor the electronic properties (e.g., the density of state near the Fermi level, d-band center, and conductivity) of Pt active sites via the hybridization of Pt 5d orbitals and O 2p orbitals. As a result, a-PtTe₂ NSs with large amounts of exposed Pt active sites and optimized binding strength to hydrogen intermediates exhibit excellent activity and stability in hydrogen evolution reaction. This article is protected by copyright. All rights reserved.

Pt Atom on the Wall of Atomic Layer Deposition (ALD)-Made MoS2 Nanotubes for Efficient Hydrogen Evolution

Single-atom catalysts (SACs) can achieve excellent catalytic efficiency at ultralow catalyst consumptions. Herein, platinum (Pt) atoms are fixed on the wall of atomic layer deposition (ALD)-made molybdenum disulfide nanotube arrays (MoS₂ -NTA) for efficient hydrogen evolution reaction (HER). More concretely, MoS₂ -NTA with different nanotube diameters and wall thicknesses are fabricated by a sacrificial strategy of anodic aluminum oxide (AAO) template via ALD; then Pt atoms are fixed on the wall of Ti₃ C₂ -supported MoS₂ -NTA as a catalytic system. The MoS₂ -NTA/Ti₃ C₂ decorated with 0.13 wt.% of Pt results in a low overpotential of 32 mV to deliver a current density of 10 mA cm^-2 , which is superior to 20 wt.% commercial Pt/C (41 mV). Ordered MoS₂ -NTA instead of 2D MoS₂ prevents Pt atoms from aggregating and then exerts catalytic activities. The density functional theory calculations suggest that the Pt atoms are more likely to occupy the sites on the tubular MoS₂ than the planar MoS₂ , and the Pt atoms accumulated at the Mo site of MoS₂ -NT have a moderate Gibbs free energy (close to zero).

Photocatalytic CO2 Reduction and Electrocatalytic H2 Evolution over Pt(0,II,IV)-Loaded Oxidized Ti Sheets

Energy recycling and production using abundant atmospheric CO₂ and H₂O have increasingly attracted attention for solving energy and environmental problems. Herein, Pt-loaded Ti sheets were prepared by sputter-deposition and Pt⁴⁺-reduction methods, and their catalytic activities on both photocatalytic CO₂ reduction and electrochemical hydrogen evolution were fully demonstrated. The surface chemical states were completely examined by X-ray photoelectron spectroscopy before and after CO₂ reduction. Gas chromatography confirmed that CO, CH₄, and CH₃OH were commonly produced as CO₂ reduction products with total yields up to 87.3, 26.9, and 88.0 μmol/mol, respectively for 700 °C-annealed Ti under UVC irradiation for 13 h. Pt-loading commonly negated the CO₂ reduction yields, but CH₄ selectivity was increased. Electrochemical hydrogen evolution reaction (HER) activity showed the highest activity for sputter-deposited Pt on 400 °C-annealed Ti with a HER current density of 10.5 mA/cm² at −0.5 V (vs. Ag/AgCl). The activities of CO₂ reduction and HER were found to be significantly dependent on both the nature of Ti support and the oxidation states (0,II,IV) of overlayer Pt. The present result could provide valuable information for designing efficient Pt/Ti-based CO₂ recycle photocatalysts and electrochemical hydrogen production catalysts.

Efficient All-2D Amorphous Cobalt Sulfide Nanosheets/Multilayered Molybdenum Disulfide Hybrid Heterojunction Catalyst for Electrochemical Hydrogen Evolution

Hydrogen energy is considered to be a critical environmentally friendly and widely sourced renewable energy source that can be used as an alternative to fossil fuels. At present, the preparation of hydrogen (H2) mainly depends on traditional fossil fuels. In order to achieve sustainable development of environmental protection, great attention has been paid to the preparation of H2 by electrocatalysis, photocatalysis, and photoelectrochemistry. Here, it is reported for the first time that a novel active catalyst for the hydrogen evolution reaction, consisting of all-2D amorphous nanosheets/2D crystal layer heterojunction structure and without any noble metal (no precious metals are present in the preparation or measuring), is almost entirely fabricated by laser ablation in liquid (LAL) growth of amorphous cobalt sulfide on the surface of multilayered molybdenum disulfide. In acidic media, the amorphous cobalt sulfide nanosheets/multilayered molybdenum disulfide (a-CoS/MoS2) catalyst exhibits fast hydrogen evolution kinetics with onset potential of -147 mV and a Tafel slope of 126 mV per decade, which is much better than only the amorphous cobalt sulfide and molybdenum disulfide layer. The high hydrogen evolution activity of the amorphous cobalt sulfide nanosheets/multilayered molybdenum disulfide hybrid is likely due to the unique electrocatalytic synergistic effects between hydrogen evolution-active amorphous cobalt sulfide nanosheets and layered crystal molybdenum disulfide materials, as well as the much-increased catalytic sites. This work provides a new general route based on all-2D amorphous nanosheets/2D crystal structure for designing and preparing novel layered materials with effectively manipulated catalytic properties and active functionality surface.

Identifying the Activation Mechanism and Boosting Electrocatalytic Activity of Layered Perovskite Ruthenate

SrRuO₃ as a rare conductive perovskite ruthenate has attracted increasing attention for application in energy conversion. Here, the electrocatalytic activity for the hydrogen evolution reaction (HER) of thermally synthesized layered SrRuO₃ is investigated and shows a considerable activation during cathodic polarization in alkaline solution. The analysis demonstrates the electrode activation is caused by the increased hydrophilicity of SrRuO₃ surface, revealing the influence of the surface properties on HER performance. For further improving the catalytic activity of perovskite ruthenate, the RuO₂ /SrRuO₃ (RSRO) heterostructure is fabricated in situ by reducing the thermal decomposition temperature of 1000 °C for SrRuO₃ to 600 °C. The appropriate lattice parameter of SrRuO₃ ensures a good lattice match, which results in a strong interaction between SrRuO₃ and RuO₂ . Hence, the RSRO substantially outperforms the corresponding single-component oxides. In addition, the increased active sites induced by the rapid improvement of hydrophilicity of RSRO surface further highlight its structural advantage for catalytic hydrogen generation. The experimental and theoretical computation results consistently validate the positive synergistic effect among SrRuO₃ and RuO₂ in tuning the atomic and electronic configuration.

Morphological Engineering of CVD-Grown Transition Metal Dichalcogenides for Efficient Electrochemical Hydrogen Evolution

2D layered transition metal dichalcogenides (TMDCs) have emerged as new possibilites beyond conventional particulate catalysts in facilitating efficient electrochemical hydrogen evolution. This is mainly mediated by the ultrahigh surface-to-volume ratio and the effective coupling of all active sites with supporting electrodes. Especially, the facile chemical vapor deposition (CVD) method has enabled morphological engineering of monolayer TMDC catalysts toward development of abundant active edge sites within the 2D plane. Here, two pathways to achieve such purpose are highlighted, either by non-equilibrium growth of MoS2 dendrites or throughout high-density nucleation of MoS2 nanoflakes directly on the electrode materials. Furthermore, future research directions have also been proposed and discussed to further enhance the efficiency of such unique catalysts.

29/2016)

On page 6207, Y. Zhang, Z. Liu and co-workers describe morphologically engineered 2D-MoS2 for the facilitation of efficient hydrogen evolution reaction. Two pathways to achieve such a purpose are highlighted, either by non-equilibrium growth of MoS2 dendrites or by high-density nucleation of MoS2 nanoflakes directly on the electrode materials. Future research directions are also proposed and discussed to further enhance the efficiency of such unique catalysts.