Zhiyong Tang

A self-sponsored doping approach for controllable synthesis of S and N co-doped trimodal-porous structured graphitic carbon electrocatalysts

A facile self-sponsored doping approach is developed to synthesize S and N co-doped trimodal-porous structured graphitic carbon network electrocatalysts. It utilizes a sole precursor (1-allyl-2-thiourea) to realize a precisely controlled co-doping of S and N during a concurrent graphitic carbon growth process by simple control of the pyrolysis temperature. The results reveal that the doping effect is heavily dependent on the doping density and a maximal catalytic activity could only be achieved with an optimal doping level. The presence of a macro-pore structure in the trimodal-porous network enhances the mass transport, enabling the full utilization of large surface areas created by micro- and meso-pores. The resultant electrocatalyst possesses high ORR catalytic activity with excellent durability and high resistance to the inhibition effect of fuel molecules. The findings of this work would be valuable for design and fabrication of high performance carbon-based electrocatalysts.

One-step solid phase synthesis of a highly efficient and robust cobalt pentlandite electrocatalyst for the oxygen evolution reaction

Cobalt pentlandite (Co9S8) has recently emerged as an alternative non-noble metal based electrocatalyst for the oxygen evolution reaction (OER). Co9S8 is known for its intrinsic structural and electronic properties favorable for electrocatalytic applications, but the synthesis of stoichiometrically optimal Co9S8 electrocatalysts remains challenging. Herein, a facile one-step solid phase calcination approach is presented in which Co9S8 nanoparticles (NPs) were concurrently synthesised on carbon nanosheets (CNSs). The reaction mechanism for this synthesis was systematically investigated using TG/DSC-MS analysis. Relative to other cobalt chalcogenide electrocatalysts, the as-prepared thermally stable nanocomposite (Co9S8/CNS) has better electrocatalytic performance for the OER in alkaline electrolytes, exhibiting a smaller overpotential of 294 mV at a current density of 10 mA cm−2 with a Tafel slope of 50.7 mV dec−1. Furthermore, a minimum overpotential of 267 mV with a Tafel slope of 48.2 mV dec−1 could be achieved using highly conducting multi-walled carbon nanotubes (MWCNTs) as a conducting filler in the nanocomposites.

Strongly Coupled CoCr2O4/Carbon Nanosheets as High Performance Electrocatalysts for Oxygen Evolution Reaction

A strongly coupled CoCr2 O4 /carbon nanosheet composite is concurrently grown via a facile one-step molten-salt calcination approach. The strong coupling between carbon and CoCr2 O4 has improved the electrical conductivity and preserved the active sites in catalysts. These results may pave the way to improve the performance of spinel oxides as electrocatalysts for oxygen evolution reactions.

Carbon-encapsulated heazlewoodite nanoparticles as highly efficient and durable electrocatalysts for oxygen evolution reactions

The activity and durability of electrocatalysts are important factors in their practical applications, such as electrocatalytic oxygen evolution reactions (OERs) used in water splitting cells and metal–air batteries. In this study, a novel electrocatalyst, comprising few-layered graphitic carbon (~5 atomic layers) encapsulated heazlewoodite (Ni3S2@C) nanoparticles (NPs), was designed and synthesized using a one-step solid phase pyrolysis method. In the OER test, the Ni3S2@C catalyst exhibited an overpotential of 298 mV at a current density of 10 mA·cm–2, a Tafel slope of 51.3 mV·dec–1, and charge transfer resistance of 22.0 Ω, which were better than those of benchmark RuO2 and most nickel-sulfide-based catalysts previously reported. This improved performance was ascribed to the high electronic conductivity of the graphitic carbon encapsulating layers. Moreover, the encapsulation of graphitic carbon layers provided superb stability without noticeable oxidation or depletion of Ni3S2 NPs within the nanocomposite. Therefore, the strategy introduced in this work can benefit the development of highly stable metal sulfide electrocatalysts for energy conversion and storage applications, without sacrificing electrocatalytic activity.

Ultrathin Transition Metal Dichalcogenide/3d Metal Hydroxide Hybridized Nanosheets to Enhance Hydrogen Evolution Activity

The vast majority of the reported hydrogen evolution reaction (HER) electrocatalysts perform poorly under alkaline conditions due to the sluggish water dissociation kinetics. Herein, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS2 and WS2 ). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH)2 and Co(OH)2 hybridized ultrathin MoS2 and WS2 nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The 2D-MoS2 /Co(OH)2 hybrid achieves an extremely low overpotential of ≈128 mV at 10 mA cm-2 in 1 m KOH. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides.

Remarkably enhanced water splitting activity of nickel foam due to simple immersion in a ferric nitrate solution

The development of a facile method to construct a high-performance electrode is of paramount importance to the application of alkaline water electrolysis. Here, we report that the activity of nickel foam (NF) towards the oxygen evolution reaction (OER) can be enhanced remarkably through simple immersion in a ferric nitrate (Fe(NO3)3) solution at room temperature. During this immersion process, the oxidation of the NF surface by NO3− ions increases the near-surface concentrations of OH− and Ni2+, which results in the in situ deposition of a highly active amorphous Ni-Fe hydroxide (a-NiFeOxHy) layer. Specifically, the OER overpotential of the NF electrode decreases from 371 mV (bare NF) to 270 mV (@10 mA·cm−2 in 0.1 M KOH) after immersion in a 20 mM Fe(NO3)3 solution for just 1 min. A longer immersion time results in further increased OER activity (196 mV@10 mA·cm−2 in 1 M KOH). The overall water splitting properties of the a-NiFeOxHy@NF electrode were evaluated using a two-electrode configuration. It is worth noting that the current density can reach 25 mA·cm−2 in 6 M KOH at an applied voltage of 1.5 V at room temperature.