Zhangping Shi

Porous nanoMoC@graphite shell derived from a MOFs-directed strategy: an efficient electrocatalyst for the hydrogen evolution reaction

The hydrogen evolution reaction using noble-metal free electrocatalysts has captured increasing attention due to its importance in renewable hydrogen production. Herein, a highly active and stable electrocatalyst of MoC encapsulated by graphitized carbon shells (nanoMoC@GS) has been developed via an in situ carburization of a Mo-based metal–organic framework (Mo-MOF) with the atomic periodic structure. The ultrafine MoC nanoparticles (∼3 nm) confined by 1–3 layered graphite shells significantly favor the efficient HER in both acidic and basic media. In particular, a low overpotential (η10 = 124 and 77 mV at a current density of −10 mA cm−2), a small Tafel slope (43 and 50 mV dec−1) and a high exchange current density (j0 = 0.015 and 0.212 mA cm−2) are achieved on nanoMoC@GS in 0.5 M H2SO4 and 1.0 M KOH, respectively. Such remarkable activity, outperforming most current noble-metal-free electrocatalysts, stems from the cooperative/synergistic effects of ultrafine MoC nanostructure, ultrathin and conductive graphitized carbon shells, and enriched porosity. This work demonstrates a feasible way to design high-performance electrocatalysts via converting “atomic contact” hybrid structures (e.g., MOFs), illustrating a new perspective for developing nanocatalysts in the energy chemistry field.

Phosphorus-Mo2C@carbon nanowires toward efficient electrochemical hydrogen evolution: composition, structural and electronic regulation

To explore high-performance electrocatalysts, electronic regulation on active sites is essentially demanded. Herein, we propose controlled phosphorus doping to effectively modify the electronic configuration of nanostructured Mo2C, accomplishing a benchmark performance of noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER). Employing MoOx–phytic acid–polyaniline hybrids with tunable composition as precursors, a series of hierarchical nanowires composed of phosphorus-doped Mo2C nanoparticles evenly integrated within conducting carbon (denoted as P-Mo2C@C) are successfully obtained via facile pyrolysis under inert flow. Remarkably, P-doping into Mo2C can increase the electron density around the Fermi level of Mo2C, leading to weakened Mo–H bonding toward promoted HER kinetics. Further density functional theory calculations show that the negative hydrogen-binding free energy (ΔGH*) on pristine Mo2C gradually increases with P-doping due to electron transfer and steric hindrance by P on the Mo2C surface, indicating the effectively weakened strength of Mo–H. With optimal doping, a ΔGH* approaching 0 eV suggests a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, the P-Mo2C@C nanowires with controlled P-doping (P: 2.9 wt%) deliver a low overpotential of 89 mV at a current density of −10 mA cm−2 and striking kinetic metrics (onset overpotential: 35 mV, Tafel slope: 42 mV dec−1) in acidic electrolytes, outperforming most of the current noble-metal-free electrocatalysts. Elucidating feasible electronic regulation and the remarkably enhanced catalysis associated with controlled P-doping, our work will pave the way for developing efficient noble-metal-free catalysts via rational surface engineering.

Microwave-Assisted Reactant-Protecting Strategy toward Efficient MoS2 Electrocatalysts in Hydrogen Evolution Reaction

The exposure of rich active sites is crucial for MoS2 nanocatalysts in efficient hydrogen evolution reaction (HER). However, the active (010) and (100) planes tend to vanish during preparation because of their high surface energy. Employing the protection by thiourea (TU) reactant, a microwave-assisted reactant-protecting strategy is successfully introduced to fabricate active-site-rich MoS2 (AS-rich MoS2). The bifunctionality of TU, as both a reactant and a capping agent, ensures rich interactions for the effective protection and easy exposure of active sites in MoS2, avoiding the complicated control and fussy procedure related to additional surfactants and templates. The as-obtained AS-rich MoS2 presents the superior HER activity characterized by its high current density (j = 68 mA cm(-2) at -300 mV vs RHE), low Tafel slope (53.5 mV dec(-1)) and low onset overpotential (180 mV), which stems from the rich catalytic sites and the promoted conductivity. This work elucidates a feasible way toward high performance catalysts via interface engineering, shedding some light on the development of emerging nanocatalysts.

Electrospinning Hetero-Nanofibers of Fe3C-Mo2C/Nitrogen-Doped-Carbon as Efficient Electrocatalysts for Hydrogen Evolution

Heterostructured electrocatalysts with multiple active components are expected to synchronously address the two elementary steps in the hydrogen evolution reaction (HER), which require varied hydrogen-binding strength on the catalyst surface. Herein, electrospinning followed by a pyrolysis is introduced to design Fe3 C-Mo2 C/nitrogen-doped carbon (Fe3 C-Mo2 C/NC) hetero-nanofibers (HNFs) with tunable composition, leading to abundant Fe3 C-Mo2 C hetero-interfaces for synergy in electrocatalysis. Owing to the strong hydrogen binding on Mo2 C and the relatively weak one on Fe3 C, the hetero-interfaces of Fe3 C-Mo2 C remarkably promote HER kinetics and intrinsic activity. Additionally, the loose and porous N-doped carbon matrix, as a result of Fe-catalyzed carbonization, ensures the fast transport of electrolytes and electrons, thus minimizing diffusion limitation. As expected, the optimized Fe3 C-Mo2 C/NC HNFs afforded a low overpotential of 116 mV at a current density of -10 mA cm-2 and striking kinetics metrics (onset overpotential: 42 mV, Tafel slope: 43 mV dec-1 ) in 0.5 m H2 SO4 , outperforming most recently reported noble-metal-free electrocatalysts.

Enhancing Metal-Support Interactions by Molybdenum Carbide: An Efficient Strategy toward the Chemoselective Hydrogenation of α,β-Unsaturated Aldehydes.

Metal-support interactions are desired to optimize the catalytic turnover on metals. Herein, the enhanced interactions by using a Mo2C nanowires support were utilized to modify the charge density of an Ir surface, accomplishing the selective hydrogenation of α,β-unsaturated aldehydes on negatively charged Ir(δ-) species. The combined experimental and theoretical investigations showed that the Ir(δ-) species derive from the higher work function of Ir (vs. Mo2C) and the consequently electron transfer. In crotonaldehyde hydrogenation, Ir/Mo2C delivered a crotyl alcohol selectivity as high as 80%, outperforming those of counterparts (<30%) on silica. Moreover, such electronic metal-support interactions were also confirmed for Pt and Au, as compared with which, Ir/Mo2C was highlighted by its higher selectivity as well as the better activity. Additionally, the efficacy for various substrates further verified our Ir/Mo2C system to be competitive for chemoselective hydrogenation.

Organic template-free synthesis of zeolite mordenite nanocrystals through exotic seed-assisted conversion

Seed-assisted synthesis has been demonstrated as a green and facile route to produce useful zeolites with several frameworks, and meanwhile shows the potential to selectively template the formation of specific structured crystals. In view of the difficulty of directly synthesizing zeolite mordenite (MOR) with short 1D, 12-MR channels, we proposed a plausible synthetic route of exotic seed-assisted conversion (ESAC), starting from aluminosilicate gel containing zeolite beta (BEA) seeds to MOR nanocrystals. Through judiciously adjusting the synthetic conditions, including NaF/Si, OH−/Si, hydrothermal temperature and added zeolite BEA seeds, nano-crystallite assembled zeolite MOR nanoparticles with rich inter-crystallite mesoporosity, high crystallinity, perfect framework, and high catalytic activity for low-density polyethylene cracking, were fast transformed under a low seeded, organic template-free system. The combined investigation of synthetic conditions and the crystallization process deepened the understanding on this special crystallization behaviour.

Tailoring Zeolite ZSM-5 Crystal Morphology/Porosity through Flexible Utilization of Silicalite-1 Seeds as Templates: Unusual Crystallization Pathways in a Heterogeneous System

Diffusion limitation in micropores of zeolites leads to a demand for optimization of zeolite morphology and/or porosity. However, tailoring crystallization processes to realize targeted morphology/porosity is a major challenge in zeolite synthesis. On the basis of previous work on the salt-aided, seed-induced route, the template effect of seeds on the formation of micropores, mesopores and even macropores was further explored to selectively achieve desired hierarchical architectures. By carefully investigating the crystallization processes of two typical samples with distinct crystal morphologies, namely, 1) nanocrystallite-oriented self-assembled ZSM-5 zeolite and 2) enriched intracrystal mesoporous ZSM-5 zeolite, a detailed mechanism is proposed to clarify the role of silicalite-1 seeds in the formation of diverse morphologies in a salt-rich heterogeneous system, combined with the transformation of seed-embedded aluminosilicate gel. On the basis of these conclusions, the morphologies/porosities of products were precisely tailored by deliberately adjusting the synthesis parameters (KF/Si, tetrapropylammonium bromide/Si and H2 O/Si ratios and type of organic template) to regulate the kinetics of seed dissolution and seed-induced recrystallization. This work may not only provide a practical route to control zeolite crystallization for tailoring crystal morphology, but also expands the knowledge of crystal growth mechanisms in a heterogeneous system.

Controlled nitridation of tantalum (oxy)nitride nanoparticles towards optimized metal-support interactions with gold nanocatalysts

The electron regulation on supports can vary metal-support interactions with loaded metals in heterogeneous catalysis. In this paper, a facile Sr2+-mediated ionothermal route was introduced to control the nitridation degree in tantalum (oxy)nitrides, resulting in varied electronic properties and optimized interactions with gold nanocatalysts. A new mechanism was proposed that the formation of SrTa4O11 intermediates facilitated the replacement of O by N in controlled nitridation, and more importantly avoided undesired over-nitridation. As expected, the TaON support with defined nitridation promoted electronic metal-support interactions to generate Auδ− species, which was highly active for the thermal hydrogenation of nitrobenzene due to the moderated adsorption and effective activation on Auδ− in Au/TaON. This work elucidated the optimized metal-support interactions achieved on controllably nitridated supports, opening up new opportunities for the development of efficient nanocatalysts.

Bimetallic Platinum-Tin Nanoparticles on Hydrogenated Molybdenum Oxide for the Selective Hydrogenation of Functionalized Nitroarenes

The hydrogenation of functionalized nitroarenes to the corresponding anilines is of great importance in the fine chemical industry and requires high‐performance catalysts with a good activity and selectivity. Herein, hydrogenated MoOx (H‐MoOx) supported bimetallic Pt‐Sn (Pt‐Sn/H‐MoOx) was developed to accomplish selective and efficient hydrogenation. In the case of 4‐nitrostyrene, an outstanding selectivity to 4‐vinylaniline (≈93 %) with a high turnover frequency (0.094 s−1) was achieved under mild conditions (T=30 °C, P H2 =1 atm). The metal–support interactions contributed to the efficient turnover on the ultrafine nanoparticles, and the atom‐rearranged bimetallic Pt‐Sn surface promoted the selectivity because of the preferred adsorption of the nitro group. The good efficiency for various functionalized nitroarenes further verified the promise of Pt‐Sn/H‐MoOx in chemoselective hydrogenation.

Structural Design and Electronic Modulation of Transition-Metal-Carbide Electrocatalysts toward Efficient Hydrogen Evolution

As the key of hydrogen economy, electrocatalytic hydrogen evolution reactions (HERs) depend on the availability of cost-efficient electrocatalysts. Over the past years, there is a rapid rise in noble-metal-free electrocatalysts. Among them, transition metal carbides (TMCs) are highlighted due to their structural and electronic merits, e.g., high conductivity, metallic band states, tunable surface/bulk architectures, etc. Herein, representative efforts and progress made on TMCs are comprehensively reviewed, focusing on the noble-metal-like electronic configuration and the relevant structural/electronic modulation. Briefly, specific nanostructures and carbon-based hybrids are introduced to increase active-site abundance and to promote mass transportation, and heteroatom doping and heterointerface engineering are encouraged to optimize the chemical configurations of active sites toward intrinsically boosted HER kinetics. Finally, a perspective on the future development of TMC electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials in energy chemistry.