Oxygen‑Coordinated Single Mn Sites for Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction reaction has attracted increasing attention due to its goal of low carbon emission and environmental protection.Here,we report an efficient NitRR catalyst composed of single Mn sites with atomically dispersed oxygen(O)coordination on bacterial cellulose-converted graphitic carbon(Mn-O-C).Evidence of the atomically dispersed Mn-(O-C_(2))_(4)moieties embedding in the exposed basal plane of carbon surface is confirmed by X-ray absorption spectroscopy.As a result,the as-synthesized Mn-O-C catalyst exhibits superior NitRR activity with an NH_(3)yield rate(RNH_(3))of 1476.9±62.6μg h^(−1)cm^(−2)at−0.7 V(vs.reversible hydrogen electrode,RHE)and a faradaic efficiency(FE)of 89.0±3.8%at−0.5 V(vs.RHE)under ambient conditions.Further,when evaluated with a practical flow cell,Mn-O-C shows a high RNH_(3)of 3706.7±552.0μg h^(−1)cm^(−2)at a current density of 100 mA cm−2,2.5 times of that in the H cell.The in situ FT-IR and Raman spectroscopic studies combined with theoretical calculations indicate that the Mn-(O-C_(2))_(4)sites not only effectively inhibit the competitive hydrogen evolution reaction,but also greatly promote the adsorption and activation of nitrate(NO_(3)^(−)),thus boosting both the FE and selectivity of NH_(3)over Mn-(O-C_(2))_(4)sites.

A COMBINED MEASUREMENT SYSTEM FOR UV/V IN SITU SPECTROELECTROCHEMICAL STUDY

A microcomputer-based UV/V in situ spectroelectrochemical measurement system has been developed.This paper presents a description of the experimental details regarding the methods and equipment.

IN SITU METALLOGRAPHIC OBSERVAION OF THERMALCYCLING EFFECTS ON PHASE TRANSFORMATION IN Cu-Zn-Al SHAPE MEMORY ALLOY

In this paper, an in situ metallographic video system was used to study the morphology in Cu-Zn-Al shape memory alloy (SMA) during thermal cycling phase tmnsforma-tion. There are seven different types of martensite morphology in Cu-Zn-Al SMA,i.e. plate, spean bamboo, noose, round-spot, line and dot-like martensites. During transformation and inverse-transformation, the thermoelastic martensites were rising and falling, growing and shrinking, splitting and merping. The growth patterns of thermoelastic martensite were divided into three types: fast growing, very slow ex-pansion and uniform automatic growth. Automatic growth appeared when ageing at a temperature below Ms. The result, for the first time, coofirmed Olson and Cohen,s suggestion that thermoelastic martensite may be automatically grown when ageing be-low Ms. With increasing numbers of thermal cycling, both the memory recovery ratio (% )and memory recoverp degradation (%) degraded logarithmically. The degrada-tion was steep in the initial stage and then became more and more gradual in the middle and the final stages caused by the stabilisation of martensite. In the initial stage, vacancies assumed the controlling role, while dislocations took the major role in other stages. The martensite transformation caused the intedeces to become bent and blurmd, but with increasing cycling numbers, the movements of interface had the same degradation effects as the memory recovery ratio curves. Under these conditions, we also found the martensites on one side of the intedece became reorientated and par-allel to the intedece. It was therefore concluded that the movement degradation of the interface and the appearance of bamboo like martensite induced the degradation of two way shape memory effect (TWMP).

Accelerated intermediate conversion through nickel doping into mesoporous Co-N/C nanopolyhedron for efficient ORR

Engineering non-precious metals into nitrogen-doped carbon is employed to improve electrocatalyst activity towards oxygen reduction reaction(ORR). A nickel-doped Co-N/C mesoporous nanopolyhedron is successfully evoluted from a Ni-doped ZIF-67 precursor. The Ni & Co synergistic N/C catalyst exhibits a half-wave potential of 0.895 V(vs. reversible hydrogen electrode(RHE)) with a diffusion-limiting current density of 6.1 m A cm^(-2)for alkaline ORR at 1600 r min^(-1), which is competitive to commercial Pt/C in terms of cost, methanol tolerance, and long-term stability. In situ surface-enhanced Raman scattering(SERS) study reveals the formation and fast conversion of superoxide ion(O_(2)^(-)) intermediate on the catalyst surface. Density functional theory(DFT) calculations demonstrate the decrease of energy barrier for potential-determining step(O* protonation) by Co-Ni synergy as well as the reduction of adsorption energy on catalyst surface upon nickel doping. The joint results of in situ SERS study and DFT calculations suggest a favourable ORR process on nickel-doped Co-N/C.