Recent advances in active sites identification and regulation of M-N/C electro-catalysts towards ORR

Transition metal and nitrogen co-doped carbon(M–N/C) catalysts are recognized as the most prospective alternatives for platinum-based electro-catalysts towards oxygen reduction reaction(ORR) in polymer electrolyte fuel cells. Recently, significant progress has been achieved in the identification and regulation of active sites of this kind of catalysts. In this mini review,we summarize the techniques and strategies to identify active sites in M–N/C catalysts, the main debates on active sites types, the measurement method for active site density, the reactivity descriptors for M–N/C catalysts, and directions to the design of ORR M–N/C catalysts.

Synthesis of nitrocarbazole compounds and their electrocatalytic oxidation of alcohol

Three compounds with nitrocarbazole frameworks were synthesized and their electrochemical reversibility as organic electrocatalysts was studied by cyclic voltammetry. The electrochemical reversibility and oxidation‐reduction potential of the compounds were greatly affected by their substituents. The oxidation‐reduction potential of the compound with an electron‐donating group was negative, while that of the compound with an electron‐withdrawing group on the carbazole framework was positive. The electrocatalytic oxidation activities of the nitrocarbazole compounds were investigated through cyclic voltammetry and controlled potential electrolysis at room tem‐perature. The electrocatalysts showed excellent selectivity for p‐methoxybenzyl alcohol, converting it to the corresponding aldehyde through electro‐oxidation with just 2.5 mol%of the electrocata‐lysts presented. The electrocatalysts maintained their excellent electroredox activity following re‐cycling.

Prospects and challenges of graphene based fuel cells

Novel characteristics of graphene have captured great attention of researchers for energy technology applications.Incorporation of graphene related hybrid and composite materials have demonstrated high performance and durability for fuel cell energy conversion devices.This article overviews graphene based materials for fuel cell technology applications such as electrodes additives,bipolar plates and proton conducting electrolyte membrane.The graphene dispersion over electrodes has revealed enhanced exposure of electrochemically active surface area for improved electro-catalytic activity towards fuel oxidation and oxidant reduction reactions.The issue of device stack durability and degraded performance due to corrosion of bipolar plates is discussed by incorporating graphene based materials.In proton exchange membrane devices,graphene as an electrolyte has shown an excellent performance towards high ionic conductivity and power density.The graphene incorporation in fuel cell devices has exhibited commendable performance and has bright future for commercial applications.

Fe/N-doped mesoporous carbons derived from soybeans: A highly efficient and low-cost non-precious metal catalyst for ORR

Oxygen reduction reaction(ORR)plays a crucial role in many energy storage and conversion devices.Currently,the development of inexpensive and high-performance carbon-based non-precious-metal ORR catalysts in alkaline media still gains a wide attention.In this paper,the mesoporous Fe-N/C catalysts were synthesized through SiO2-mediated templating method using biomass soybeans as the nitrogen and carbon sources.The SiO2 templates create a simultaneous optimization of both the surface functionalities and porous structures of Fe-N/C catalysts.Detailed investigations indicate that the Fe-N/C3 catalyst prepared with the mass ratio of SiO2 to soybean being 3:4 exhibits brilliant electrocatalytic performance,excellent long-term stability and methanol tolerance for the ORR,with the onset potential and the half-wave potential of the ORR being about 0.890 V and 0.783 V(vs RHE),respectively.Meanwhile,the desired 4-electron transfer pathway of the ORR on the catalysts can be observed.It is significantly proposed that the high BET specific surface area and the appropriate pore-size,as well as the high pyridinic-N and total nitrogen loadings may play key roles in enhancing the ORR performance for the Fe-N/C3 catalyst.These results suggest a feasible route based on the economical and sustainable soybean biomass to develop inexpensive and highly efficient non-precious metal electrochemical catalysts for the ORR.

Platinum in-situ catalytic oleylamine combustion removal process for carbon supported platinum nanoparticles

Colloidal synthesis method such as oleylamine(OAm)-stabilized process is of great interest for obtaining uniform and highly dispersed platinum nanoparticle catalysts, yet the ligand may unavoidably inhibit their electro-catalytic performance. Thus, fully removing these ligands is critical to activate catalyst surface. Previous research of OAm removal process pointed that thermal annealing was the most effective way in comparison with other methods such as chemical washing, UV–Ozone irradiation and cyclic voltammetry sweeping, but generally resulting in undesired growth of platinum nanoparticle. Few studies concerning a more efficient ligand removal process have been published yet. In this work we proposed a platinum in-situ catalytic OAm combustion strategy to elucidate the removal mechanism of OAm ligands in thermal process and the key experimental parameters were also optimized. In addition, heat flow signal based on differential scanning calorimetry(DSC) measurement as a sensitive indicator, is suggested to reveal the ligand removal efficiency, which is much more reliable than the traditional spectroscopy.In comparison with commercial Pt/C sample, such a surface clean Pt/C electrocatalyst has shown an enhanced specific activity for oxygen reduction reaction. Our removal strategy and the evaluation method are highly instructive to efficient removal of different organic ligands.

Preparation and application of electro-catalytic material Fe_2O_3-ZnO/C

Electro-catalysts Fe203 compounded by ZnO were prepared by a sol-gel method, which were titled as Fe203-ZnO. Electro-catalysts Fe203-ZnO loading on the bamboo charcoal was titled as Fe203-ZnO/C. The catalytic materials were characterized by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The obtained catalysts were assembled to three-dimensional electrodes to degradation of chlorinated organic in paper wastewater. And the performance tests show that three-dimensional electrodes have high activities for degradation of chlorinated organic in paper wastewater. There are many factors affecting the electro-catalytic performances of the three-dimensional electrodes. And the orthogonal experiment results show that the optimum operating condition is as follows： the calcination time of the catalysts 2 h, the mass ratio of Fe to Zn 4：1, the voltage 12 V, the mass of the catalytic materials 6 g, the value of pH 9, and the treating time 2.5 h. Under these conditions, the optimum removal efficiency of chlorinated organics in paper wastewater is 47.58%.

Synthesis and characterization of ZnO-Al_2O_3 oxides as energetic electro-catalytic material for glucose fuel cell

One of the thrust areas of research is to find an alternative fuel to meet the increasing demand for energy.Glucose is a good source of alternative fuel for clean energy and is easily available in abundance from both naturally occurring plants and industrial processes.Electrochemical oxidation of glucose in fuel cell requires high electro-catalytic surface of the electrode to produce the clean electrical energy w ith minimum energy losses in the cell.Pt and Pt based alloys exhibit high electro-catalytic properties but they are expensive.For energy synthesis at economically cheap price,non Pt based inexpensive high electro catalytic material is required.Electro synthesized Zn O-Al2O3composite is found to exhibit high electro-catalytic properties for glucose oxidation.The Cyclic Voltammetry and Chronoamperometry curves reflect that the material is very much comparable to Pt as far as the maximum current and the steady state current delivered from the glucose oxidation are concerned.XRD image confirms the mixed oxide composite.SEM images morphology show increased 3D surface areas at higher magnification.This attributed high current delivered from electrochemical oxidation of glucose on this electrode surface.

Oxygen Electroreduction Performance of Ultrasmall Gold Nanoclusters

Ultrasmall gold nanoclusters consisting of 2-4 Au atoms were synthesized and their per- formance in electrocatalytic oxygen reduction reactions （ORR） was examined. These clus- ters were synthesized by exposing AuPPh3Cl to the aqueous ammonia medium for one week. Electrospray ionization mass spectrometry （ESI-MS）, X-ray absorption fihe struc- ture （XAFS）, and X-ray photoelectron spectroscopy （XPS） analyses indicate that the as- synthesized gold clusters （abbreviated as Aux） consist of 2-4 Au atoms coordinated by the triphenylphosphine, hydroxyl, and adsorbed oxygen ligands. A glassy carbon disk electrode loaded with the Aux clusters （Aux/GC） was characterized by the cyclic and linear-sweep voltammetry for ORR. The cyclic voltammogram vs. RHE shows the onset potential of 0.87 V, and the kinetic parameters of JK at 0.47 V and the electron-transfer mmlber per oxygen molecule were calculated to be 14.28 mA/cm2 and 3.96 via the Koutecky-Levich equations, respectively.

Nanostructured amorphous Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) high-entropy-alloy:an efficient electrocatalyst for oxygen evolution reaction

Proximal configu ration of dissimilar metal atoms in amorphous high-entropy-alloys(HEAs) always re sult in interatomic d-band ligand effect,dense defect distribution,coordinatively unsaturated sites,high potential energy,and loose atom bonding.Herein,nanostructured amorphous Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) HEA ribbon is fabricated via a melt spinning method combined with electrochemical corrosion etching process,which is applied as the potential oxygen evolution reaction electrocatalyst.It is found that there are micro/nano pits on the surface of etched amorphous Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) ribbons.Various elements of HEAs bond with each other to form a highly disordered configu ration,which could result in an optimized bonding energy and enhanced intrinsic catalytic activity.The electrocatalysis activity measurements indicate that the amorphous HEA endows a much higher activity than the crystalline one,which is further improved by the electrochemical etching treatment.Especially,the HEA ribbon etched for 3 h requires a low overpotential of 230 mV to afford 10 mA cm^(-2) current density.In addition,density functional theory calculations demonstrate that the amorphous structure can weaken the interaction between the surface of Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) alloy and the intermediates,leading to an optimized adsorption Gibbs free energy.

Synthesis of composition-tunable octahedral Pt–Cu alloy nanocrystals by controlling reduction kinetics of metal precursors

In this paper, we reported a solvothermal method for the synthesis of octahedral Pt-Cu bimetallic alloy nanocrystals （NCs） with tunable composition. Inspired by the result from our previous exploration on octahedral Pt-Cu alloy NCs that Cu contents can be tuned from 10 % to 50 %, we further tuned the Cu portion from 50 % to 75 % by simply introducing n-butylamine in the reaction system. It is believed that n-butylamine plays a key role in breaking through a thermodynamic constraint in the formation of Pt-Cu alloy nanocrystals （NCs）. The synergistic effect of underpotential deposition-like Cu reduction and the different complexion abilities of amine group of n-butylamine with two metal species effectively tuned the reduction kinetics, by which each reduced Pt atom is able to catalyze reduction of more Cu atoms and be fully covered with 12 Cu atoms in the Pt-Cu alloy crystal, while Cu precursor is not able to be reduced solely and bind solely with Cu atoms, resulting in the successful tuning of Cu composition from 50 % to 75 %. In addition, we investigated the electro-catalytic activity of Pt-Cu bimetallic alloy NCs with different composition in electro-oxidation of methanol. The as-prepared PtCu3 NCs exhibit excellent electro-catalytic performance and stability in comparison with commercial Pt black and other compositional Pt-Cu alloy NCs.