Gaopeng Jiang

Co-N Decorated Hierarchically Porous Graphene Aerogel for Efficient Oxygen Reduction Reaction in Acid.

Nitrogen-functionalized graphene materials have been demonstrated as promising electrocatalyst for the oxygen reduction reaction (ORR), owning to their respectable activity and excellent stability in alkaline electrolyte. However, they exhibit unacceptable catalytic activity in acid medium. Here, a hierarchically porous Co-N functionalized graphene aerogel is prepared as an efficient catalyst for the ORR in acid electrolyte. In the preparation process, polyaniline (PANI) is introduced as a pore-forming agent to aid in the self-assembly of graphene species into a porous aerogel networks, and a nitrogen precursor to induce in situ nitrogen doping. Therefore, a Co-N decorated graphene aerogel framework with a large surface area (485 m(2) g(-1)) and an abundance of meso/macropores is effectively formed after heat treatment. Such highly desired structures can not only expose sufficient active sites for the ORR but also guarantee the fast mass transfer in the catalytic process, which provides significant catalytic activity with positive onset and half wave potentials, low hydrogen peroxide yield, high resistance to methanol crossover, and remarkable stability that is comparable to commercial Pt/C in acid medium.

Quaternized Graphene Oxide Nanocomposites as Fast Hydroxide Conductors

Nanocomposites play a key role in performance improvements of hydroxide conductors employed in a wide range of alkaline-electrochemical systems such as fuel cells and metal-air batteries. Graphene oxide (GO) nanosheets are considered to be outstanding nanofillers for polymeric nanocomposites on account of their excellent physicochemical strength and electrochemical properties. In this work, a fast hydroxide conductor was developed on the basis of a chemically modified GO nanocomposite membrane. The high surface area of GO was functionalized with highly stable hydroxide-conductive groups using a dimethyloctadecyl [3-(trimethoxysilyl)propyl]ammonium chloride (DMAOP) precursor, named QAFGO, and then composed with porous polybenzimidazole PBI (pPBI) as a well-suited polymeric backbone. The nanocomposite exhibited outstanding hydroxide conductivity of 0.085 S cm(-1), high physicochemical strength, and electrochemical stability for 21 days. An alkaline fuel cell (AFC) setup was fabricated to determine the functionality of QAFGO/pPBI nanocomposite in an alkaline-based system. The high AFC performance with peak power density of 86.68 mW cm(-2) demonstrated that QAFGO/pPBI nanocomposite membrane has promising potential to be employed as a reliable hydroxide conductor for electrochemical systems working in alkaline conditions.

In Situ Polymer Graphenization Ingrained with Nanoporosity in a Nitrogenous Electrocatalyst Boosting the Performance of Polymer-Electrolyte-Membrane Fuel Cells

Rich, porous graphene frameworks decorated with uniformly dispersed active sites are prepared by using polyaniline as a graphene precursor and introducing phenanthroline as a pore-forming agent. The unprecedented fuel-cell performance of this electrocatalyst is linked to the graphene frameworks with vast distribution of pore sizes, which maximizes the active-sites accessibility, facilitates mass-transport properties, and improves the carbon corrosion resistance.

Theoretical insight into highly durable iron phthalocyanine derived non-precious catalysts for oxygen reduction reactions

N4-chelate macrocycles comprise the foundation for non-precious metal oxygen reduction reaction (ORR) catalyst research, where the main electrochemical process occurs in polymer electrolyte membrane (PEM) fuel cells. Although iron–nitrogen–carbon (M–N–C) complexes are known to be the most active non-precious ORR catalysts to date, a fundamental understanding of the ORR mechanisms of these materials is still in its nascent stage and needs further investigation. In this work, ab initio density functional theory (DFT) calculations have been applied to unveil the underlying principles for the electrocatalytic activity and structural stability of Fe–N4 chelates exposed to acidic media. Therefore, we compared the electronic structures of ferrous phthalocyanine (Fe-Pc) and an in-house developed Fe-Pc modified with diphenylphenthioether substituent species (Fe-SPc). The results of these DFT simulations directly correlate with the results of the half-cell ORR activity and stability electrochemical testing in 0.1 M HClO4. The results indicate that the relative energetic position of the dz2-orbital with respect to the Fermi level can induce an Fe redox couple potential shift and modulate the catalytic activity towards the ORR. Furthermore, our combined DFT calculations and empirical observations highlight that the relative position of the dz2-orbital can be controlled by the incorporation of functional groups, resulting in the ability to tune the ORR activity of these complexes. Structural stability of the materials, as predicted by the DFT-calculated cohesive energies of Fe and FeO, can also be readily tuned by modulating Fe-Pc with the substituent species. This study, coupling rigorous experimental observations with DFT investigations, thereby provides a fundamental insight that can aid in the design of future generations of non-precious ORR catalysts with improved activity and stability.

Nitrogen-doped carbon nanocones encapsulating with nickel–cobalt mixed phosphides for enhanced hydrogen evolution reaction

In this work, nickel–cobalt mixed metal phosphides encapsulated into nitrogen-doped carbon nanocones (Ni2P/NiCoP@NCCs) have been prepared through a facile ammonia-etching of nickel–cobalt Prussian blue analogs (Ni–Co PBAs) followed by a subsequent phosphidation treatment. During the in situ and confined phosphidation process, very small nickel–cobalt mixed metal phosphide nanocrystallites are uniformly incorporated into the simultaneously produced nitrogen-doped carbon matrix. Due to the unique structure and composition, the resultant Ni2P/NiCoP@NCCs possess high electrocatalytic activity and excellent durability for the HER in both acidic and alkaline solutions.

Molecular Functionalization of Graphene Oxide for Next-Generation Wearable Electronics

Acquiring reliable and efficient wearable electronics requires the development of flexible electrolyte membranes (EMs) for energy storage systems with high performance and minimum dependency on the operating conditions. Herein, a freestanding graphene oxide (GO) EM is functionalized with 1-hexyl-3-methylimidazolium chloride (HMIM) molecules via both covalent and noncovalent bonds induced by esterification reactions and electrostatic πcation-π stacking, respectively. Compared to the commercial polymeric membrane, the thin HMIM/GO membrane demonstrates not only slightest performance sensitivity to the operating conditions but also a superior hydroxide conductivity of 0.064 ± 0.0021 S cm(-1) at 30% RH and room temperature, which was 3.8 times higher than that of the commercial membrane at the same conditions. To study the practical application of the HMIM/GO membranes in wearable electronics, a fully solid-state, thin, flexible zinc-air battery and supercapacitor are made exhibiting high battery performance and capacitance at low humidified and room temperature environment, respectively, favored by the bonded HMIM molecules on the surface of GO nanosheets. The results of this study disclose the strong potential of manipulating the chemical structure of GO to work as a lightweight membrane in wearable energy storage devices, possessing highly stable performance at different operating conditions, especially at low relative humidity and room temperature.

An all-aqueous redox flow battery with unprecedented energy density

Redox flow batteries are of particular interest because of the flexible power and energy storage originating from their unique architecture, but their low energy density has inhibited their widespread dissemination. In this work, a novel strategy of tuning the pH of the electrolyte environment is put forward to enhance the battery voltage, and eventually achieve the goal of high energy density for all-aqueous redox flow batteries. With this strategy, a hybrid alkaline zinc–iodine redox flow battery has been designed with a 0.47 V potential enhancement by switching the anolyte from acidic to basic, thus inspiring an experimental high energy density of 330.5 W h L−1. This is an unprecedented record to date for an all-aqueous redox flow battery.

A Lithium-Sulfur Battery using a 2D Current Collector Architecture with a Large-Sized Sulfur Host Operated under High Areal Loading and Low E/S Ratio

While backless freestanding 3D electrode architectures for batteries with high loading sulfur have flourished in the recent years, the more traditional and industrially turnkey 2D architecture has not received the same amount of attention. This work reports a spray-dried sulfur composite with large intrinsic internal pores, ensuring adequate local electrolyte availability. This material offers good performance with a electrolyte content of 7 µL mg-1 at high areal loadings (5-8 mg cm-2 ), while also offering the first reported 2.8 µL mg-1 (8 mg cm-2 ) to enter into the second plateau of discharge and continue to operate for 20 cycles. Moreover, evidence is provided that the high-frequency semicircle (i.e., interfacial resistance) is mainly responsible for the often observed bypassing of the second plateau in lean electrolyte discharges.