Zhicai Xing

Recent Progress in Cobalt-Based Heterogeneous Catalysts for Electrochemical Water Splitting

Water electrolysis is considered as the most promising technology for hydrogen production. Much research has been devoted to developing efficient electrocatalysts for hydrogen production via the hydrogen evolution reaction (HER) and oxygen production via the oxygen evolution reaction (OER). The optimum electrocatalysts can drive down the energy costs needed for water splitting via lowering the overpotential. A number of cobalt (Co)-based materials have been developed over past years as non-noble-metal heterogeneous electrocatalysts for HER and OER. Recent progress in this field is summarized here, especially highlighting several important bifunctional catalysts. Various approaches to improve or optimize the electrocatalysts are introduced. Finally, the current existing challenges and the future working directions for enhancing the performance of Co-implicated electrocatalysts are proposed.

Closely Interconnected Network of Molybdenum Phosphide Nanoparticles: A Highly Efficient Electrocatalyst for Generating Hydrogen from Water

A closely interconnected network of MoP nanoparticles (MoP-CA2) with rich nano-pores, large specific surface area, and high conductivity can function as a highly active non-noble metal catalyst for electrochemically generating hydrogen from acidic water. The network exhibits nearly 100% Faradaic efficiency and needs overpotentials of 125 and 200 mV to attain current densities of 10 and 100 mA cm(-2) , respectively. The catalytic activity is maintained for at least 24 h.

FeP Nanoparticles Film Grown on Carbon Cloth: An Ultrahighly Active 3D Hydrogen Evolution Cathode in Both Acidic and Neutral Solutions

In this Letter, we demonstrate the direct growth of FeP nanoparticles film on carbon cloth (FeP/CC) through low-temperature phosphidation of its Fe3O4/CC precursor. Remarkably, when used as an integrated 3D hydrogen evolution cathode, this FeP/CC electrode exhibits ultrahigh catalytic activity comparable to commercial Pt/C and good stability in acidic media. This electrode also performs well in neutral solutions. This work offers us the most cost-effective and active 3D cathode toward electrochemical water splitting for large-scale hydrogen fuel production.

Two-dimensional hybrid mesoporous Fe2O3–graphene nanostructures: A highly active and reusable peroxidase mimetic toward rapid, highly sensitive optical detection of glucose

In this article, for the first time, two-dimensional hybrid mesoporous Fe2O3-graphene (mFe2O3-G) nanostructures were developed as a peroxidase mimetic with catalytic activities superior to those of mFe2O3, G, and previously reported Fe-based peroxidase mimetics. The high-surface-area mFe2O3 not only offers a large number of catalytically active sites, but also facilitates the diffusion of 3,3,5,5-tetramethylbenzidine (TMB) and H2O2 toward G surface. On the other hand, G is π-rich and thus favors the adsorption and enrichment of TMB within these pores. These synergistic effects lead to highly improved catalytic performances. Based on these findings, a simple, rapid, and highly sensitive and selective optical detector of glucose has been developed and demonstrated in buffer solution with a pretty low detection limit of 0.5 μM. In addition, this nanosensor is reusable and can also be used for glucose detection in diluted serum.

Three-Dimensional Structures of MoS2@Ni Core/Shell Nanosheets Array toward Synergetic Electrocatalytic Water Splitting

Hydrogen evolution reaction (HER) in alkaline media using non-noble metal catalysts with great efficiency represents a critical challenge in current water-alkaline and chlor-alkali electrolyzers. Herein, we demonstrate that the MoS2@Ni core/shell nanosheets array vertically aligned on carbon cloth (MoS2@Ni/CC) is a highly active electrocatalyst for HER. In alkaline solutions, MoS2@Ni/CC needs overpotentials of 91, 118, and 196 mV to approach current densities of 10, 20, and 100 mA cm(-2), respectively, exceeding behavior of commercial Pt/C catalyst at high current densities. Additionally, this catalyst also exhibits excellent electrocatalytic activity toward HER in neutral electrolytes. Such high hydrogen evolution activities are due to synergistic electrocatalytic effects between MoS2 core and Ni shell.

Interconnected Co‐Entrapped, N‐Doped Carbon Nanotube Film as Active Hydrogen Evolution Cathode over the Whole pH Range

The use of electrocatalysts with low metal content (metal-deficient) or metal free for the hydrogen evolution reaction (HER) can prevent or decrease metal ion release, which reduces environmental impact; development of such catalysts with high activity and durability over the whole pH range is thus highly desired but still remains a huge challenge. Herein, we describe the direct growth of a film consisting of interconnected Co-entrapped, N-doped carbon nanotubes on carbon cloth using chemical vapor deposition from dicyanodiamine using a Co3 O4 nanowire array as catalyst. This integrated architecture is used as a flexible 3D electrode for the electrolytic hydrogen evolution with outstanding catalytic activity and durability in acidic media. Moreover, this electrode is also highly efficient under neutral and basic conditions. It offers us an attractive carbon-based metal-deficient HER catalyst outperforming most transition-metal and all metal-free/deficient catalysts.

One-pot green hydrothermal synthesis of CuO–Cu2O–Cu nanorod-decorated reduced graphene oxide composites and their application in photocurrent generation

In this communication, we develop a facile one-pot green strategy toward CuO–Cu2O–Cu nanorod-decorated reduced graphene oxide (CuNRs–rGO) composites by hydrothermal heating of the mixed solution of GO and Cu(OAc)2 under basic conditions without the use of extra reducing agents. As-synthesized composites have been successfully applied in photocurrent generation in the visible spectral region.

PH-driven dissolution–precipitation: a novel route toward ultrathin Ni(OH)2 nanosheets array on nickel foam as binder-free anode for Li-ion batteries with ultrahigh capacity

In this paper, for the first time, we report on the growth of ultrathin Ni(OH)2 nanosheet arrays on a nickel foam (NF) via a novel pH-driven dissolution–precipitation route, carried out by a hydrothermal treatment of the NF in an acidic medium without the introduction of other nickel sources. Acid etching of the NF surface leads to nano-pits and produces Ni(H2O)n2+ ions at the early stage of the reaction. With the elapsed time, an increase in the pH level occurs and the Ni(H2O)n2+ ions gradually hydrolyze and preferentially precipitate on the nano-pits, serving as nucleation sites and leading to ultrathin Ni(OH)2 nanosheet arrays on an NF. The effects of the experimental parameters, such as reaction time, acid type and starting pH value, on the Ni(OH)2 growth are also investigated. Because the nano-pits are integrated parts of the NF and the deposition of Ni(OH)2 nanosheets on such nano-pits ensures intimate contact between them, the Ni(OH)2/NF is robust enough to withstand a violent sonication process and efficient and rapid electron transfer is achieved. As a binder-free anode for Li-ion batteries, the Ni(OH)2/NF exhibits an unexpected ultrahigh capacity of 1689 mA h g−1 and excellent cycling stability.

Carbon nanofiber-templated mesoporous TiO2 nanotubes as a high-capacity anode material for lithium-ion batteries

The present communication demonstrates the synthesis of uniform mesoporous TiO2 nanotubes via hydrolysis and condensation of tetrabutyl titanate (TBOT) using carbon nanofibers as templates followed by calcination under air. We further demonstrate the use of such TiO2 nanotubes as an anode material for rechargeable lithium-ion batteries (LIBs) with high discharge capacity, good rate capability and excellent cycling performance. They deliver a high discharge capacity of 209.6 mA h g−1 at a current density of 0.2 C in the voltage range 1.0–3.0 V. They can still deliver a discharge capacity of 108.1 and 88.8 mA h g−1 with 100 and 93.2% capacity retention after 500 charge–discharge cycles under current densities of 2 and 4 C, respectively.

N-Doped Carbon-Coated Tungsten Oxynitride Nanowire Arrays for Highly Efficient Electrochemical Hydrogen Evolution

It is highly desired but still challenging to develop active nonprecious metal hydrogen evolution reaction (HER) electrocatalysts operating under all pH conditions. Herein, the development of three-dimensional N-doped carbon-coated tungsten oxynitride nanowire arrays on carbon cloth as a highly efficient and durable HER cathode was explored. The material delivers current densities of 10 and 100 mA cm(-2) at overpotentials of 106 and 172 mV, respectively, in acidic medium, and it also performs well in neutral and basic electrolytes.