Qiuju Zhang

A Ni(OH)2–PtO2 hybrid nanosheet array with ultralow Pt loading toward efficient and durable alkaline hydrogen evolution

The design and development of highly active electrocatalysts for the hydrogen evolution reaction (HER) in alkaline media is of significant importance. In this communication, we report the direct growth of an ultralow-Pt-content (Pt content: 5.1 wt%) Ni(OH)2–PtO2 hybrid nanosheet array on a Ti mesh (Ni(OH)2–PtO2 NS/Ti), carried out by hydrothermal treatment of a Ni(OH)2 nanosheet array on a Ti mesh (Ni(OH)2 NS/Ti) in the presence of [PtCl6]2−. When used as a 3D catalyst electrode for the HER, the resulting Ni(OH)2–PtO2 NS/Ti exhibits superior activity with the need of an overpotential of only 31.4 mV to deliver a geometrical catalytic current density of 4 mA cm−2 in 0.1 M KOH. Remarkably, this catalyst also shows strong long-term electrochemical durability for at least 100 h with a faradaic efficiency close to 100%. Density functional theory calculations reveal that the Ni(OH)2/PtO2 interface can promote the kinetics of H2O dissociation and tune the hydrogen adsorption free energy to a more moderate value, thereby promoting the HER.

Catalyzed activation of CO2 by a Lewis-base site in W–Cu–BTC hybrid metal organic frameworks

A metal–organic framework (MOF)-based catalyst W–Cu–BTC is designed by hybridizing highly active W ions into Cu3(BTC)2(H2O)3 (also known as Cu–BTC or HKUST-1, BTC = 1,3,5-tricarboxylate benzene) frameworks based on density functional (DFT) calculations. We show that the hybrid W–Cu node plays a pivotal role in activating CO2 according to frontier molecular orbital theory. In contrast to the Lewis-acid nature of open metal sites in most MOFs, the exposed W ion in W–Cu–BTC is identified as a Lewis-base site, evidenced by the substantial electron donation from W ion to CO2. Kinetically, the linear CO2 molecule can be readily bent by forming a CO2–W complex after overcoming a negligible activation barrier of 0.09 eV. In addition, we present calculated infrared spectra (IR) and X-Ray spectra (XPS) for reference in future experimental studies.

Sol-gel Auto-combustion Synthesis of Ni-CexZr1-xO2 Catalysts for Carbon Dioxide Reforming of Methane

Carbon dioxide reforming of methane (methane dry reforming) over Ni–Ce0.8Zr0.2O2 catalysts prepared by a sol–gel auto-combustion method and a conventional co-precipitation method were comparatively studied. We show that sol–gel auto-combustion is very promising for preparing thermal stable homogeneous mixed metal oxide catalysts. The auto-combustion synthesized catalyst exhibited higher initial activity and stability due to its smaller Ni crystalline size and intimate interaction between Ni and Ce0.8Zr0.2O2. In contrast, the co-precipitated catalyst showed poor activity and deactivated rapidly. The rapid deactivation was caused by a higher graphitization degree of the deposited carbon over co-precipitated catalyst with larger Ni crystalline size. We also found that the physico-chemical properties and catalytic activity of sol–gel auto-combustion synthesized catalysts were closely related to the metal nitrate (MN)/citric acid (CA) ratio. High MN/CA ratio led to more violent combustion behaviour and an accordingly higher degree of crystallization of the synthesized catalyst. In contrast, a low MN/CA ratio resulted in more carbon species residues and poor catalytic performance. The Ce/Zr ratio also had a profound influence on the phase structure, reducibility, oxygen vacancies and catalytic performance of Ni–Ce0.8Zr0.2O2 catalysts. Ni–Ce0.8Zr0.2O2 catalyst with cubic phase exhibited the best catalytic performance because of high reducibility, high Ni dispersion and strong Ni-CexZr1−xO2 interaction, and considerable amounts of oxygen vacancies.

Cobalt-Borate Nanoarray: An Efficient and Durable Electrocatalyst for Water Oxidation under Benign Conditions

The development of efficient earth-abundant electrocatalysts for oxygen evolution reaction (OER) under benign conditions is still urgent and challenging. Herein, we report the electrochemical generation of novel Co-Bi nanoarray on carbon cloth (Co-Bi NA/CC) from CoS2 nanoarray precursor. As a three-dimensional anode, such Co-Bi NA/CC exhibits excellent electrocatalytic performance for OER with the overpotential requirement of 411 mV to drive 10 mA cm-2. Notably, this electrode also demonstrates outstanding long-term electrochemical durability for 20 h.

Synthesis and characterization of transparent polyimides derived from ester-containing dianhydrides with different electron affinities

Two series of poly(ester imide)s derived from bis(trimellitic acid anhydride) phenyl ester (TAHQ) and bis[(3,4-dicarboxylic anhydride) phenyl] terephthalate (PAHP), as well as poly(ether imide)s based on hydroquinone diphthalic anhydride (HQDPA), were synthesized with aromatic diamines via solution polycondensation. These polyimide films were transparent with an ultraviolet-visible absorption cut-off wavelength below 375 nm, and with tensile strengths of 42.0–83.8 MPa, tensile moduli of 2.5–4.7 GPa and elongations at break of 2.1–5.4%. Compared with the poly(ether imide)s, the poly(ester imide)s showed higher glass transition temperatures (Tg), lower water absorption (WA) and lower temperature of 5% weight loss (Td5%). Moreover, the poly(ester imide)s derived from PAHP with a low electron affinity of 2.04 eV by theoretical calculation achieved better transparency, lower WA and slightly lower Tg than the corresponding TAHQ-based poly(ester imide)s.

Differential Permeability of Proton Isotopes through Graphene and Graphene Analogue Monolayer

Two-dimensional (2D) monolayer nanomaterials can be exploited as the thinnest membrane with distinct differential sieving properties for proton isotopes. Motivated from the experimental evidence of differential sieving proton isotopes through graphene and hexagonal boron nitrate (h-BN) monolayer, we compute the kinetic barrier of isotope H(+) and D(+) permeation through model graphene and h-BN fragments at the MP2/6-31++G(d,p) level of theory. On the basis of the ratio of tunneling reaction rate constant, the isotope separation ratio of H(+)/D(+) and H(+)/T(+) is predicted to be ∼12 and 37, respectively. The tunneling reaction rate constant can be estimated from the zero-point-energy computed at the transition state for the proton isotope permeation though the 2D model systems. We show that the presence of Stone-Wales (55-77) defect in the model graphene fragment can significantly lower the proton permeation barrier by 0.55 eV. With the defect, the ratio of tunneling reaction rate constant of H(+)/D(+) is increased to ∼25. In addition to model graphene and h-BN, we have examined proton permeation capability of α-boron monolayer. We compute the tunneling reaction pathway for H(+) through α-boron monolayer using both the climbing nudged elastic band (c-NEB) method and the scanning-path method. Both methods suggest that α-boron monolayer entails a relatively low barrier of ∼0.20 eV for H(+) permeation, much lower than that of the model graphene and h-BN fragments. Our studies provide molecular-level insights into the differential permeation of proton isotopes through 2D materials. The methods can be extended to examine isotope separation capability of other 2D materials as well.

Selective phosphidation: an effective strategy toward CoP/CeO2 interface engineering for superior alkaline hydrogen evolution electrocatalysis

Co phosphides, although highly active for the hydrogen evolution electrocatalysis in acids, still deliver inferior performance in alkalis, limiting their application in alkaline water electrolysis. Building an effective Co phosphide/(hydroxide)oxide interface could be a viable way to improve the hydrogen evolution activity of Co phosphide catalysts under alkaline conditions, which however remains unexplored and challenging. In this communication, we report the facile development of a CoP–CeO2 hybrid nanosheet film on Ti mesh (CoP–CeO2/Ti) from easily made Co3O4–CeO2via a selective phosphidation strategy. In 1.0 M KOH, such CoP–CeO2/Ti achieves a geometrical catalytic current density of 10 mA cm−2 at a pretty low overpotential of 43 mV, 27 mV less than that for CoP/Ti. Remarkably, our CoP–CeO2/Ti also shows superior durability over CoP/Ti, suggesting that CeO2 greatly stabilizes the CoP catalyst. Density functional theory calculations demonstrate that CoP–CeO2 possesses a lower water dissociation free energy and a more optimal hydrogen adsorption free energy than CoP. This selective phosphidation strategy is universal in engineering the transition metal phosphide/oxide interface for applications.

Ultrasmall Ru2P nanoparticles on graphene: a highly efficient hydrogen evolution reaction electrocatalyst in both acidic and alkaline media

Ultrasmall ruthenium phosphide nanoparticles grown on reduced graphene oxide nanosheets (Ru2P/RGO-20) are reported as a highly efficient hydrogen evolution reaction (HER) catalyst. It achieves a current density of -10 mA cm-2 at extremely low overpotentials of -22 and -13 mV under acidic and alkaline conditions, respectively, superior to those of commercial Pt/C.

A platinum oxide decorated amorphous cobalt oxide hydroxide nanosheet array towards alkaline hydrogen evolution

We report the design of an amorphous cobalt oxide hydroxide nanosheet array with anchored platinum oxide. This electrocatalyst can efficiently catalyze the hydrogen evolution reaction with outstanding activity due to the strong synergetic effect derived from its favorable composition and structure. Density functional theory calculations further demonstrate that it can greatly reduce water dissociation barriers and tune the free energy of H* adsorption close to the optimized value.

Surface-termination-dependent Pd bonding and aggregation of nanoparticles on LaFeO3 (001)

The bonding and morphology of Pd clusters deposited on the LaO- and FeO2-terminated LaFeO3 (001) surface were studied using periodic density functional methods together with scanning transmission electron microscopy. We show that Pd tends to aggregate to three-dimensional (3D) clusters on both terminations since the Pd-Pd cohesive energy is larger than the Pd-LaFeO3 adhesive energy. However, from the kinetic point of view, Pd migration on the LaO termination is facile, while stronger interactions between Pd and the FeO2 termination significantly hinder the migration of Pd. Furthermore, molecular dynamics simulations demonstrate that Pd would agglomerate into 3D metallic and PdOx particles on the LaO and FeO2 terminations, respectively, and hint at the possibility of partial penetration of the PdOx particles into the surface, as observed experimentally.