Jinli Qiao

3-Dimensional porous N-doped graphene foam as a non-precious catalyst for the oxygen reduction reaction

Nitrogen-doped graphene materials have been demonstrated as promising alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries due to their relatively high activity and good stability in alkaline solutions. However, they suffer from low catalytic activity in acid medium. Herein, we have developed an efficient ORR catalyst based on nitrogen doped porous graphene foams (PNGFs) using a hard templating approach. The obtained catalyst exhibits both remarkable ORR activity and long term stability in both alkaline and acidic solutions, and its ORR activity is even better than that of the Pt-based catalyst in alkaline medium. Our results demonstrate a new strategy to rationally design highly efficient graphene-based non-precious catalysts for electrochemical energy devices.

A flexible solid-state electrolyte for wide-scale integration of rechargeable zinc–air batteries

Rechargeable zinc–air batteries, having high energy densities and cost-effectiveness, are important environmentally-benign energy storage solutions. Here we developed a facile strategy for fabricating a nanoporous alkaline-exchange electrolyte membrane from natural cellulose nanofibres, exhibiting high ionic-conductivity and water retention as well as high bending flexibility. These advantages render the membrane a promising solid-state electrolyte for rechargeable zinc–air batteries in lightweight and flexible electronic applications.

Aqueous CO2 reduction on morphology controlled CuxO nanocatalysts at low overpotential

Various CuxO catalysts with different special microstructures were synthesized using a simple one-step hydrothermal method by controlling the reaction time and temperature conditions. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) were used to observe the morphologies of the received catalysts. The 3-dimensional (3D) hierarchical nanospheres (500 nm) comprised of secondary structured nanorods (50 nm) are formed at 180 °C for 2 hours. However, when increasing the hydrothermal reaction temperature to 220 °C, solid microspheres with a large size of 2.5 μm begin to appear instead of flabby hierarchical nanospheres. To further investigate the effect of morphologies on the activity and production selectivity of CuxO catalysts, cyclic voltammetry (CV) was used to evaluate the onset potential and current density of catalyzed CO2 reduction combining linear sweep voltammetry (LSV) in 0.5 M KHCO3 solution. The effect of catalyst loading was also tested by applying the gas diffusion layer (GDL) to make up a working electrode for CO2 electroreduction. The results indicate that the synthesized temperature of 180 °C for 2 h is the optimal condition for CuxO nanospheres and the optimal loading is about 3 mg cm−2, under which the onset potential for CO2 electroreduction reaches −0.55 V vs. SHE. By ion chromatography measurement, the faradaic efficiency and production rate of produced formate was found to be 59%, which is much higher than most reported Cu-based catalysts at the same electrolysis conditions, indicating the high selectivity of the CuxO nanospheres due to their controlled special surface morphology.

A large-scale synthesis of heteroatom (N and S) co-doped hierarchically porous carbon (HPC) derived from polyquaternium for superior oxygen reduction reactivity

A simple, large-scale and green synthetic route is demonstrated for the preparation of polyquaternium derived heteroatom (N and S) co-doped hierarchically porous carbon (HPC). Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of (N and S) co-doped carbon (N–S-HPC). As a result, the obtained N–S-HPC shows a superior catalytic ORR performance to the commercial Pt/C catalyst in alkaline media, including high catalytic activity, remarkable long-term stability and strong methanol tolerance. Even in acidic media where most non-precious metal catalysts suffer from high overpotential and low durability, our N–S-HPC exhibits an amazing ORR activity with a half-wave potential of 0.73 V, and 40% enhanced limited diffusion-current density when compared to the Pt/C catalyst. Particularly, when used for constructing a zinc–air battery cathode, such an N–S-HPC catalyst can give a discharge peak power density as high as 536 mW cm−2. At 1.0 V of cell voltage, a current density of 317 mA cm−2 is achieved. This performance is superior to all reported non-precious metal catalysts in the literature for zinc–air batteries and significantly outperforms the state-of-the-art platinum-based catalyst.

Improvement of the performance of polymer/C60 photovoltaic cells by small-molecule doping

The performance of polymer/C 60 photovoltaic cells doped with organic small molecules is investigated. It is shown that the small molecules with better hole-transporting mobility are helpful to the performance improvement of photovoltaic cells, while those molecules with better electron-transporting mobility are not. Hole-transporting material, triplephenylamine (TPA), is found to be the best dopant in the photovoltaic cells compared with the cells (MEH-PPV:C 60 =1:1) without the dopant. With the addition of 40% (w/w) TPA, the short-circuit current increases five folds, and the white-light energy conversion efficiency reaches 0.24%.

Electrochemical CO2 reduction to formic acid on crystalline SnO2 nanosphere catalyst with high selectivity and stability

A novel catalyst for CO 2 electroreduction based on nanostructured SnO 2 was synthesized using a facile hydrothermal self-assembly method. The electrochemical activity showed that the catalyst gave outstanding catalytic activity and selectivity in CO 2 electroreduction. The catalytic activity and formate selectivity depended strongly on the electrolyte conditions. A high faradaic efficiency, i.e., 56%, was achieved for formate formation in KHCO 3 (0.5 mol/L). This is attributed to control of formate production by mass and charge transfer processes. Electrolysis experiments using SnO 2 -50/GDE (an SnO 2 -based gas-diffusion electrode, where 50 indicates the 50% ethanol content of the electrolyte) as the catalyst, showed that the electrolyte pH also affected CO 2 reduction. The optimum electrolyte pH for obtaining a high faradaic efficiency for formate production was 8.3. This is mainly because a neutral or mildly alkaline environment maintains the oxide stability. The faradaic efficiency for formate production declined with time. X-ray photoelectron spectroscopy showed that this is the result of deposition of trace amounts of fluoride ions on the SnO 2 -50/GDE surface, which hinders reduction of CO 2 to formate.

Effects of additives on palladium nanocrystals supported on multiwalled carbon nanotubes and their electrocatalytic properties toward formic acid oxidation

Carbon nanotubes are believed to be powerful materials for constructing novel hybrid composites with desirable functionalities and applications in many fields. Therefore, a better understanding of the functionalization of multiwalled carbon nanotubes (MWCNTs) holds the key to a better performance of the hybrid properties. In this paper, with a series of aromatic bifunctional molecule additives, modified MWCNTs were used as composite supports for synthesizing nanostructured palladium catalysts for formic acid oxidation. The additives contain anthranilic acid, o-phenylenediamine, salicylic acid, catechol, and phthalic acid. The influence of the different bifunctional groups (such as –NH2, –OH, –COOH, and their mixed groups) on the morphologies, particle sizes, and electrical properties of Pd nanocrystals was intensively studied. Transmission electron microscopy measurement demonstrates that the palladium nanoparticles were well dispersed on the surface of MWCNTs with a relatively narrow particle size distribution in the presence of the additives. Cyclic voltammetry and chronoamperometry tests demonstrate that the functional groups of the additives play an important role in electrocatalytic activity and stability for formic acid oxidation, and the influence law of various functional groups on electrocatalytic activity and stability is also investigated in this paper. We hope it can provide certain theoretical guidance meaning and practical reference value in future studies.

Effect of acid-leaching on carbon-supported copper phthalocyanine tetrasulfonic acid tetrasodium salt (CuTSPc/C) for oxygen reduction reaction in alkaline electrolyte: active site studies

Although non-precious metal catalysts (NPMCs) have been extensively studied as low-cost catalyst alternatives to Pt, in particular for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs), the nature of the active ORR catalytic sites is still a subject of controversy. In this work, using carbon-supported copper phthalocyanine tetrasulfonic acid tetrasodium salt (CuTSPc/C) nanoparticles as the target catalyst, the effects of the transition metal Cu on the ORR active sites are systematically studied using both rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques in alkaline electrolyte. The results show that acid-leaching can significantly decrease the ORR activity of the CuTSPc/C catalyst, with the half-wave potential negatively shifted by more than 50 mV compared to the catalyst before acid-leaching. The electron transfer number of the ORR process catalyzed by the catalyst before acid-leaching remained at about 3.85 over the whole tested potential range from −0.6 to −0.1 V, while this number greatly decreased from 3.82 at −0.55 V to 3.53 at −0.1 V after acid-leaching. The H2O2 produced accordingly increased sharply from 7.8% to 22%. XRD and TEM results indicate that acid-leaching is an effective method to remove metal-Cu. XPS analysis reveals that metal-Cu is essential in the ORR active site structure, and also plays a key part in the stabilization of the active N and S species.

Using aminopyrine as a nitrogen-enriched small molecule precursor to synthesize high-performing nitrogen doped mesoporous carbon for catalyzing oxygen reduction reaction

With aminopyrine as a nitrogen-enriched small molecule precursor, a series of nitrogen doped carbon materials have been fabricated and explored as electrocatalysts for oxygen reduction reaction (ORR). The most active catalyst is a nitrogen doped carbon, which was prepared through a facile template-mediated pyrolyzing method using ferric nitrate (Fe(NO3)3·9H2O) as an activation reagent along with nanoscaled silica as a sacrificial support (hereafter referred to as AP/SiO2). The AP/SiO2 is confirmed and identified as having highly active molecule catalytic centers for ORR, due to its possessing a porous, sponge-like and uniform structure with a super-large specific surface area of 932.68 m2 g−1. The AP/SiO2 catalyst exhibited a high onset potential of 0.98 V, a half-wave potential of 0.82 V, and a high number of exchanged electrons (>3.8, close to four) in alkaline media. After 5000 continuous cycles, the material showed almost no negative shift with respect to the Pt/C material. Even in acidic medium, the AP/SiO2 catalyst still showed much higher durability than Pt/C and a low yield of HO2−. This work may have provided a new and simple route in the design and batch-synthesis of highly active and durable carbonaceous electrocatalysts for ORR.

Bi-functional composite electrocatalysts consisting of nanoscale (La, Ca) oxides and carbon nanotubes for long-term zinc–air fuel cells and rechargeable batteries

Here, we report a new nanocomposite based on (La, Ca) oxides, which exhibits superior bi-functional activity and durability in a zinc–air battery with an everlasting discharge peak power density achieving long life (750 cycles). This work opens a new avenue for the design/fabrication of durable bi-functional electrocatalysts for scaleable applications in zinc–air batteries.