Influence of counter electrode material during accelerated durability test of non-precious metal electrocatalysts in acidic medium

Significant progress has been made in the development of non-precious metal electrocatalysts （NPMEs） during the past decade. Correspondingly, there is an urgent demand for an appropriate measurement method to be established for the reliable evaluation of NPMEs. In this study, platinum and graphite counter electrodes were used to investigate the impact of counter electrode material on the accelerated durability testing （ADT） of NPMEs in acidic medium. Platinum used as the coun- ter electrode in a traditional three-electrode electrochemical cell was found to dissolve in acidic medium and re-deposit on NPME coated on the working electrode during ADT. Such re-deposition causes the oxygen reduction reaction （ORR） performance of NPMEs to remarkably improve, and thus will seriously mislead our judgment of NPMEs if we are unaware of it. The phenomenon can be avoided using a graphite counter electrode.

看书琐记

今之图书,能逃出“无错不成书”之厄者,寥寥也。然古之善本,亦未能免。兹举《风俗通义》为例。藏于北图之元大德间刻本,因原版断裂,印工无识,将卷第九节一叶上截三字印于第二叶,而将第二叶上截三字印于第一叶,遂不可向读。瞿镛铁琴铜剑楼,宋、元善本甲于吴中,然收藏之《风俗通义》,

Selective synthesis of Sb2S3 nanostructures with different morphologies for high performance in dye-sensitized solar cells

In this work,we initially synthesized Sb2S3 with uniform flower-like structures via a facile hydrothermal method through the modification of the Sb source and pH value.Afterward,Sb2S3 with a nanosheet structure was successfully synthesized on reduced graphene oxide(Sb2S3@RGO).The flower-like Sb2S3 and the Sb2S3@RGO nanosheets were tested as the counter electrode(CE)of dye-sensitized solar cells,and the latter exhibited a higher electrocatalytic property than the former owing to the introduction of graphene.The results from electrochemical tests indicated that the as-prepared Sb2S3@RGO nanosheets possess higher catalytic activity,charge-transfer ability,and electrochemical stability than Sb2S3,RGO,and Pt CEs.More notably,the power conversion efficiency of Sb2S3@RGO reached 8.17%,which was higher than that of the standard Pt CE(7.75%).

Transition‐metal‐atom‐pairs deposited on g‐CN monolayer for nitrogen reduction reaction:Density functional theory calculations

The development of highly active DFT catalysts for an electrocatalytic N_(2)reduction reaction(NRR)under mild conditions is a difficult challenge.In this study,a series of atom‐pair catalysts(APCs)for an NRR were fabricated using transition‐metal(TM)atoms(TM=Sc−Zn)doped into g‐CN monolayers.The electrochemical mechanism of APCs for an NRR has been reported by well‐defined density functional theory calculations.The calculated limiting potentials were−0.47 and−0.78 V for the Fe_(2)@CN and Co_(2)@CN catalysts,respectively.Owing to its high suppression of hydrogen evolution reactions,Co_(2)@CN is a superior electrocatalytic material for a N_(2)fixation.Stable Fe_(2)@CN may be a strongly attractive material for an NRR with a relatively low overpotential after an improvement in the selectivity.The two‐way charge transfer affirmed the donation‐acceptance procedure between N_(2)and Fe_(2)@CN or Co_(2)@CN,which play a crucial role in the activation of inert N≡N bonds.This study provides an in‐depth investigation into atom‐pair catalysts and will open up new avenues for highly efficient g‐CN‐based nanostructures for an NRR.

Structural and mechanistic understanding of an active and durable graphene carbocatalyst for reduction of 4-nitrophenol at room temperature

The development of an active, durable, and metal-free carbocatalyst that is able to replace metal-based catalysts is of increasing scientific and technological importance. The use of such a catalyst would avoid problems caused by metal- containing catalysts, for example, environmental pollution by heavy metals and depletion of rare metal resources. Herein, an active and durable graphene carbocatalyst is presented for the carbocatalytic conversion of 4-nitrophenol to 4-aminophenol at ambient temperature. The carbocatalyst was prepared via a mild, water-based reaction between L-ascorbic acid （AA） and graphene oxide （GO） and did not involve any other reactants. During the structure and catalytic property optimization, a series of carbocatalysts were fabricated at various reaction temperatures and AA/GO ratios. Using several characterization techniques, detailed structural features of these carbocatalysts were identified. Possible active species and sites on the carbocatalysts were also identified such as certain oxygen-containing groups, the ~x-conjugated system, and graphene sheet edges. In addition, the synergistic effect between these active species and sites on the resulting catalytic activity is highlighted. Furthermore, we clarified the origin of the high stability and durability of the optimized carbocatalyst. The work presented here aids the design of high-performance carbocatalysts for hydrogenation reactions, and increases understanding of the structural and mechanistic aspects at the molecular level that lead to high catalyst activity and durability.

Advanced Asymmetrical Supercapacitors Based on Graphene Hybrid Materials

Supercapacitors operating in aqueous solutions are low cost energy storage devices with high cycling stability and fast charging and discharging capabilities, but generally suffer from low energy densities. Here, we grow Ni（OH）2 nanoplates and RuO2 nanoparticles on high quality graphene sheets in order to maximize the specific capacitances of these materials. We then pair up a Ni（OH）2/graphene electrode with a RuO2/graphene electrode to afford a high performance asymmetrical supercapacitor with high energy and power density operating in aqueous solutions at a voltage of -1.5 V. The asymmetrical supercapacitor exhibits significantly higher energy densities than symmetrical RuO2-RuO2 supercapacitors or asymmetrical supercapacitors based on either RuO2- carbon or Ni（OH）2-carbon electrode pairs. A high energy density of -48 W.h/kg at a power density of -0.23 kW/kg, and a high power density of -21 kW/kg at an energy density of N14 W-h/kg have been achieved with our Ni（OH）2/graphene and RuO2/graphene asymmetrical supercapacitor. Thus, pairing up metal-oxide/graphene and metal-hydroxide/graphene hybrid materials for asymmetrical supercapacitors represents a new approach to high performance energy storage.

Graphene-Based Conducting Inks for Direct Inkjet Printing of Flexible Conductive Patterns and Their Applications in Electric Circuits and Chemical Sensors

A series of inkjet printing processes have been studied using graphene-based inks. Under optimized conditions, using water-soluble single-layered graphene oxide （GO） and few-layered graphene oxide （FGO）, various high image quality patterns could be printed on diverse flexible substrates, including paper, poly（ethylene terephthalate） （PET） and polyimide （PI）, with a simple and low-cost inkjet printing technique. The graphene-based patterns printed on plastic substrates demonstrated a high electrical conductivity after thermal reduction, and more importantly, they retained the same conductivity over severe bending cycles. Accordingly, flexible electric circuits and a hydrogen peroxide chemical sensor were fabricated and showed excellent performances, demonstrating the applications of this simple and practical inkjet printing technique using graphene inks. The results show that graphene materials--which can be easily produced on a large scale and possess outstanding electronic properties--have great potential for the convenient fabrication of flexible and low-cost graphene- based electronic devices, by using a simple inkjet printing technique.

Oscillating Guided Modes in Graphene-Based Asymmetric Waveguides

We investigate the guided modes in monolayer graphene-based waveguides with asymmetric quantum well structure induced by unequal dc voltages. The dispersion relation for the guided modes is obtained analytically, the structures of the guided modes are discussed under three distinct cases. For the cases of the classical motion and the Klein tunneling, the asymmetric structure does not influence the mode structures dramatically compared with that in the symmetric waveguide. But for the mixing case of the former two, the mode structures and the motion characteristics for the electron and the hole exhibit different behaviors at same condition. The results may be helpful for the practical application of graphene-based quantum devices.