H.-J. Qiu

Nanoporous Graphene with Single‐Atom Nickel Dopants: An Efficient and Stable Catalyst for Electrochemical Hydrogen Production

Single-atom nickel dopants anchored to three-dimensional nanoporous graphene can be used as catalysts of the hydrogen evolution reaction (HER) in acidic solutions. In contrast to conventional nickel-based catalysts and graphene, this material shows superior HER catalysis with a low overpotential of approximately 50 mV and a Tafel slope of 45 mV dec(-1) in 0.5 M H2SO4 solution, together with excellent cycling stability. Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp-d orbital charge transfer between the Ni dopants and the surrounding carbon atoms. The resultant local structure with empty C-Ni hybrid orbitals is catalytically active and electrochemically stable.

Designed synthesis of hollow Co3O4 nanoparticles encapsulated in a thin carbon nanosheet array for high and reversible lithium storage

The design and fabrication of novel composite nano-architectures is crucial for their applications in energy storage devices such as lithium ion batteries (LIBs). Herein, a thin carbon nanosheet array with encapsulated hollow Co3O4 nanoparticles is successfully fabricated on 3D Ni foam by using electrodeposited Co(OH)2 nanosheets as templates and followed by a two step annealing process. When used as an anode material in LIBs, the hollow Co3O4/carbon nanosheet composite displays an excellent performance with a high reversible capacity, excellent cycling stability and rate capability. This work is helpful for the design of an advanced electrode for LIBs, supercapacitors, electrochemical sensors, etc.

Designed synthesis of cobalt-oxide-based nanomaterials for superior electrochemical energy storage devices

Cobalt oxides, such as Co3O4 and CoO, have received increasing attention as potential anode materials for rechargeable lithium-ion batteries (LIBs) owing to their high theoretical capacity. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials for LIBs. In this review, we summarize recent developments in the rational design and fabrication of various cobalt oxide-based nanomaterials and their lithium storage performance, including 1D nanowires/belts, 2D nanosheets, 3D hollow/hierarchical structures, hybrid nanostructures with carbon (amorphous carbon, carbon nanotubes and graphene) and mixed metal oxides. By focusing on the effects of their structure on their electrochemical performance, effective strategies for the fabrication of cobalt oxide/carbon hybrid nanostructures are highlighted. This review shows that by rational design, such cobalt-oxide-based nanomaterials are very promising as next generation LIB anodes.

Novel peapod array of Ni2P@graphitized carbon fiber composites growing on Ti substrate: a superior material for Li-ion batteries and the hydrogen evolution reaction

A novel one-dimensional (1-D) peapod array of nickel phosphide (Ni2P)@graphitized carbon fiber composites consisting of graphitized carbon fiber and the encapsulated Ni2P nanoparticles has been designed and synthesized on titanium foil substrate. This smart and elaborate architecture design offers several remarkable advantages, including large interfacial area, short charge transporting path, strong physical adhesion with the current collector and large electrolyte diffusion pathway between the peapod array. When used for lithium ion batteries, excellent electrochemical performances such as a high capacity of 634 mA h g−1 at a current density of 200 mA g−1, long-term cycling stability and outstanding rate capability, are obtained. In 0.5 M sulfuric acid, as an electrocatalyst for hydrogen evolution reaction, the peapod array of Ni2P@graphitized carbon fiber composites gives a current density of 10 mA cm−2 at a small over-potential of 45 mV and a small Tafel slope of ∼46 mV decade−1. More importantly, the sample exhibits exceptional stability in an acidic environment. Furthermore, it is believed that the idea to prepare the 1-D peapod array on a conductive substrate is generic and could be extended to be used with other materials.

Core–shell-structured nanoporous PtCu with high Cu content and enhanced catalytic performance

A core–shell-structured bimetallic nanoporous PtCu catalyst with a high non-noble metal content (Cu: ∼55 at%) and uniformly distributed ultrafine ligaments (∼3 nm) is fabricated by one-step dealloying a well-designed Pt4Cu21Mn75 single-phase ternary precursor in 1 M (NH4)2SO4 aqueous solution. The one-step dealloying involves a two-step corrosion process: one is fast dealloying the most active Mn from the ternary alloy to form nanoporous PtCu and the next step is a slow dealloying process which would slowly dissolve Cu from the PtCu alloy ligament surface forming a core–shell-structured nanoporous PtCu alloy with a Pt shell and a PtCu alloy core. Electrochemical measurements manifest that the core–shell-structured nanoporous PtCu exhibits greatly enhanced catalytic activity towards the electro-oxidation of methanol and formic acid compared with both nanoporous Pt and the state-of-the-art Pt/C catalyst. With evident advantages of facile preparation and enhanced catalytic performance, the nanoporous core–shell-structured PtCu catalyst is very promising as an anode catalyst in fuel cells. Moreover, this strategy (i.e., dealloying well-designed Mn-based ternary alloys) can also be used to fabricate other uniform nanoporous core–shell-structured alloys such as the nanoporous NiCu alloy.

Quasi-graphene-envelope Fe-doped Ni2P sandwiched nanocomposites for enhanced water splitting and lithium storage performance

Developing advanced graphene-based composites is significant for the development of renewable green energy technology. Herein, we report a sandwich-like graphene-based composite (i.e., Fe-doped Ni2P nanoparticles encapsulated by a graphene-like envelope), which is synthesized by the first polymerization of glucose (as a green carbon source) on the Fe-doped NiNH4PO4·H2O nanosheet surface followed by high temperature annealing. The annealing process will crystallize the coated polymer into multilayer graphene, as the same time the Fe-doped precursor is decomposed into Fe-doped Ni2P ((Fe)Ni2P) nanoparticles encapsulated by the graphene envelope ((Fe)Ni2P/graphene). When evaluated as a water splitting catalyst in acidic solutions, the graphene-encapsulated Fe-doped Ni2P exhibits a low overpotential (∼50 mV) and a small Tafel slope (∼45 mV per decade) in 0.5 M H2SO4 solution. More importantly, the (Fe)Ni2P/graphene composite shows an excellent stability in acid solutions in contrast to conventional Ni-based catalysts. On the other hand, owing to the structural advantage (i.e., efficient inner volume space for the nanoparticle expansion, high porosity for the electrolyte diffusion and high conductivity), the (Fe)Ni2P/graphene nanocomposite exhibits a high specific capacity of 642 mA h g−1 at 0.2 C and excellent cycling stability (93% retained after 200 cycles).

Nanoporous metal as a platform for electrochemical and optical sensing

Due to their extraordinary electrical and optical properties, dealloyed nanoporous metals and their derivatives have stimulated increasing interest in their sensing applications ever since dealloying was proposed to be a good strategy to fabricate uniform nanoporous metals. This article comprehensively and critically reviews the emerging nanoporous metal-based electrochemical, electronic, and optical sensors for both biological and chemical detection. We emphasize the underlying detection (or signal transduction) mechanisms, the unique roles and advantages/disadvantages of dealloyed nanoporous metals in sensing. Properties and preparations of different nanoporous metals, and their functionalizations are also highlighted in view of sensor developments. Finally, the perspective and current challenges of nanoporous metal-based sensing are outlined.

A novel monolithic three-dimensional graphene-based composite with enhanced electrochemical performance

Monolithic 3D porous graphene with a small pore size of ∼250 nm was obtained by a chemical vapor deposition method, using dealloyed nanoporous Ni as a substrate. Monolithic nanocomposites of CoO or PdCo nanoparticles decorated on the 3D porous graphene were facilely synthesized and used as an advanced anode material for lithium ion batteries or as an electrocatalyst in fuel cells, respectively. The synthesized CoO or PdCo alloy nanoparticles with narrow diameter distributions are uniformly anchored on the porous graphene inner surface. The CoO/porous graphene nanocomposite displayed a high performance in lithium ion batteries with a large reversible capacity, excellent cycling stability, and good rate performance. The PdCo/porous graphene exhibited an enhanced catalytic activity for the oxidation of ethanol compared with both Pd/porous graphene and commercial Pd/C, highlighting the importance of monolithic porous graphene in enhancing the electrochemical performance of metal and metal oxide nanoparticles.

Unique Sandwiched Carbon Sheets@Ni-Mn Nanoparticles for Enhanced Oxygen Evolution Reaction.

A unique sandwich-like architecture, where Ni-Mn nanoparticles are enveloped in coupled carbon sheets (CS@Ni-Mn), has been successfully fabricated. In the synthesis process, a great quantity of uniform NiMnO3 nanosheets generated by a universal hydrothermal method acts as precursors and templates and the cheap, environmentally friendly and recyclable glucose functions as a green carbon source. Via subsequent hydrothermal reaction and thermal annealing, sandwiched nanocomposites with Ni-Mn nanoparticles embedded inside and carbon sheets encapsulating outside can be massively prepared. The novel sandwich-like CS@Ni-Mn possesses numerous advantages, such as an intrinsic porous feature, large specific surface area, and enhanced electronic conductivity. Moreover, as a promising NiMn-based oxygen evolution reaction (OER) catalyst, the special sandwiched nanostructure demonstrates improved electrochemical properties in 1 M KOH, including a low overpotential of about 250 mV, a modest Tafel slope of 40 mV dec(-1), excellent stability over 2000 cycles, and durability for 40 h.

Enhanced electrochemical supercapacitance of binder-free nanoporous ternary metal oxides/metal electrode.

Free-standing nanoporous Ni-Cu-Mn mixed metal oxides on metal with a high surface area was fabricated by chemically dealloying a Ni8Cu12Mn80 single-phase precursor, followed by electrochemical oxidation in an alkaline solution. Electrochemical analysis shows that first Cu and Mn-based metal oxides formed by the electrochemical oxidation. Ni-based oxides grow later with the increase of electrochemical CV cycles and mix with the Cu/Mn oxides, forming a relatively stable mixed metal oxides thin film on metal ligament network. Due to the different electrochemical properties of each metal and the synergetic effect between them, the mixed ternary metal oxides formed on metal nano-ligament can operate stably between a wide potential window (1.5V) in 1.0M KOH aqueous solution when tested as a free-standing supercapacitor electrode. Due to the high volumetric surface area, wide operating potential window and excellent conductivity, the nanoporous metal oxides@metal composite exhibits a high volumetric capacitance (∼500Fcm(-3)), high energy density (∼38mWhcm(-3)) and good cycling stability.