Pingwei Cai

Oxygen‐Containing Amorphous Cobalt Sulfide Porous Nanocubes as High‐Activity Electrocatalysts for the Oxygen Evolution Reaction in an Alkaline/Neutral Medium

A novel OER electrocatalyst, namely oxygen-incorporated amorphous cobalt sulfide porous nanocubes (A-CoS4.6 O0.6 PNCs), show advantages over the benchmark RuO2 catalyst in alkaline/neutral medium. Experiments combining with calculation demonstrate that the desirable O* adsorption energy, associated with the distorted CoS4.6 O0.6 octahedron structure and the oxygen doping, contribute synergistically to the outstanding electrocatalytic activity.

Multifunctional high-activity and robust electrocatalyst derived from metal–organic frameworks

High-activity electrocatalysts with robust structure are critical for development of renewable-energy technologies. Herein, a hybrid of cobalt nanoparticles embedded in N-doped carbon nanotubes (Co@NCNT) was fabricated via economically scalable pyrolysis of a mixture of a Co-based metal–organic framework (ZIF-67) and dicyandiamide. The as-synthesized Co@NCNT hybrid was characterized by techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photon spectroscopy (XPS) etc., confirming that it possessed desirable properties of high surface area, robust structure, and good conductivity. A series of electrochemical measurements demonstrated that the Co@NCNT exhibits high activity and excellent durability toward several important electrochemical reactions, including hydrogen evolution reaction (HER) in pH-universal electrolyte, oxygen reduction reaction (ORR) in both acidic and alkaline media, glucose oxidation reaction (GOR), and oxygen evolution reaction (OER) in alkaline medium, mainly as a result of the synergistic effects of unique structure and high surface area of the Co nanoparticles and nitrogen dopant in the nanocomposite. A zinc–air battery with outstanding performance was set up using the Co@NCNT as cathode material, demonstrating its potential applications in energy storage and as a conversion system device.

In situ integration of CoFe alloy nanoparticles with nitrogen-doped carbon nanotubes as advanced bifunctional cathode catalysts for Zn–air batteries

Electrochemical catalysis of O2-incorporated reactions is a promising strategy for metal-air batteries. The performance of metal-air batteries is determined by the catalytic activities of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Therefore, developing efficient catalysts with superior activities for the ORR and OER is of great significance to expand the application range of metal-air batteries. Herein, CoFe alloy nanoparticles adhered to the inside wall of nitrogen doped carbon nanotubes (CoFe@NCNTs) are synthesized and can function as a Janus particle to efficiently catalyze the ORR and OER with desirable activities in 0.1 M KOH solution. Specifically, the CoFe@NCNTs present an onset potential of 0.95 V and a half-wave potential of 0.84 V as an ORR catalyst. When used as an air-cathode catalyst for a Zn-air battery, the CoFe@NCNTs cathode performs better than a Pt/C cathode, showing a high open-circuit potential of 1.45 V, a maximum power density of 150 mW cm-2 and an average specific capacity of 808 mA h gzn-1 at current densities from 2 mA cm-2 to 10 mA cm-2.

Robust 3D macroporous structures with SnS nanoparticles decorating nitrogen-doped carbon nanosheet networks for high performance sodium-ion batteries

There still remains a great technological challenge for the development of advanced rechargeable batteries for future electric vehicles and for storage for a more renewable energy grid. In this paper a reliable and simple method for the preparation of three-dimensional (3D) hierarchical nanohybrids with tin sulfide (SnS) nanoparticles decorating nitrogen-doped carbon nanosheet networks (SnS/N-CNNs) as an anode material for SIBs is reported. The interconnected network structure, associated with its unique porous feature, endows the developed SnS/N-CNNs with enough straining space for mitigating the effect of volume expansion upon cycling, and also ensures highly favorable transport kinetics for both electrons and sodium ions. Accordingly, the SnS/N-CNNs exhibit an outstanding electrochemical performance with a high capacity and long-term cycling performance at a high mass loading, delivering high reversible capacity of 484 and 322xa0mA h g−1 at the current rate of 1.0 and 5.0 A g−1, respectively, for 1000 cycles, running at a mass loading of 1.5 mg cm−2. Capacities of 428 and 331 mA h g−1 were obtained at the current densities of 1 A g−1 at 2.8 and 4.3 mg cm−2 loading, respectively. The first principles theoretical calculations indicated that robust binding between SnS and nitrogen-doped CNNs was of great significance for maintaining the 3D network structure that achieves high capacity, high rate capability, and superior long cyclic stability even at a high mass loading.

Alkaline–Acid Zn–H2O Fuel Cell for the Simultaneous Generation of Hydrogen and Electricity

An alkaline-acid Zn-H2 O fuel cell is proposed for the simultaneous generation of electricity with an open circuit voltage of about 1.25u2005V and production of H2 with almost 100u2009% Faradic efficiency. We demonstrate that, as a result of harvesting energy from both electrochemical neutralization and electrochemical Zn oxidation, the as-developed hybrid cell can deliver a power density of up to 80u2005mWu2009cm-2 and an energy density of 934u2005Whu2009kg-1 and maintain long-term stability for H2 production with an output voltage of 1.16u2005V at a current density of 10u2005mAu2009cm-2 .

Ferrocene-based porous organic polymer derived high-performance electrocatalysts for oxygen reduction

Two nitrogen-rich porous organic polymers (POPs) were prepared via facile and low-cost Schiff base chemistry with ferrocene (Fc) and melamine/melem as building blocks. Carbonization of these POP precursors results in porous carbon nanohybrids with carbon composites containing crystalline Fe3C/Fe. Characterization based on a variety of techniques demonstrates that the porous carbon nanohybrids feature rich-nitrogen doping, good conductivity and high BET surface area with unique porous structure, endowing them with an excellent catalytic activity toward the oxygen reduction reaction (ORR) in alkaline electrolytes. The catalysts obtained by carbonization at 800xa0°C (N-Fc-800) exhibit favorable activity with a rather high onset potential and half wave potential of 0.96 and 0.82 V, respectively. Furthermore, a rechargeable zinc-air battery was assembled using the N-Fc-800 as the cathode catalyst. Compared with the commercial Pt/C, the N-Fc-800 based battery displays a considerably high power density of 178 mW cm−2 with a smaller charge–discharge voltage gap of 0.94 V, and holds excellent stability with a less activity decay (1.0%) over long charge–discharge cycles (200 cycles).

An electrochemically neutralized energy-assisted low-cost acid-alkaline electrolyzer for energy-saving electrolysis hydrogen generation

The ability to reduce the energy consumed and the cost in water splitting is crucial for the generation of hydrogen, which can be stored and then oxidized to deliver clean, abundant, and sustainable energy with the regeneration of water. Herein, we report an asymmetric electrolyzer with three-dimensional (3D) Ni2P nanorod networks as bifunctional electrocatalysts for acidic cathode and alkaline anode that are separated by a bipolar membrane; this type of electrolyzer affords us with optimization in decreasing the energy required and maximizing the electrocatalysts: (1) pH gradient between an anolyte and a catholyte separated by a bipolar membrane provides the electrolyzer with additional electrochemical neutralization energy for facilitating water splitting and (2) efficiency of electrocatalysts can be maximized by offsetting the well-known mismatch of optimal conditions for electrocatalysts between the anode (normally alkaline) and the cathode (generally acidic). This unprecedented water electrolysis system can activate water splitting at an applied voltage of around 0.79xa0V that is significantly lower than the minimum theoretical voltage requirement (1.23 V), reducing electricity energy consumed by more than 35.8%.

A self-supported Ni–Co perselenide nanorod array as a high-activity bifunctional electrode for a hydrogen-producing hydrazine fuel cell

Although the fundamental processes of electrolytic hydrogen generation are relatively well understood, fundamental studies and explorations of the new concepts and materials for electrolysis are highly desirable to make renewable hydrogen sufficiently cost-competitive. Herein, we report a proof-of-concept for an alkaline–acid-based hydrogen generating hydrazine fuel cell by coupling the hydrazine oxidation reaction (HzOR) at the alkaline anode with the hydrogen evolution reaction (HER) at the acidic cathode. Furthermore, we verified that such a hybrid cell could simultaneously fulfill hydrogen production and electricity generation owing to harvesting of two types of electrochemical energies, i.e., electrochemical energy of the HzOR and the electrochemical neutralization energy. To this end, a bifunctional electrode comprising a three-dimensional nanoporous Ni–Co perselenide nanorod array (NixCo1−xSe) was designed and prepared by a facile two-step synthesis process, involving the initial in situ electroplating on a carbon cloth followed by subsequent selenization. The optimized electrode, i.e., Ni0.5Co0.5Se2, showed high electrocatalytic activity toward HzOR in alkaline electrolyte and HER in acidic medium. The optimized alkaline–acid hydrazine fuel cell, with the Ni0.5Co0.5Se2 electrode as both the cathode and anode, could potentially deliver a power density of 13.3 mW cm−2 at a current density of 54.7 mA cm−2 with good long-term stability and a faradaic efficiency of nearly 100% for hydrogen production.