Carbon-nitrogen/graphene composite as metal-free electrocatalyst for the oxygen reduction reaction

Sheet-like carbon-nitrogen (CNx)/graphene composites with a high content of nitrogen (x≤0.15) was prepared by the carbonization of polypyrrole (PPy)/reduced-graphene-oxide (rGO) composite at 600-800°C. We used rGO instead of graphene oxide (GO) sheets as a template and a substrate to immobilize PPy since the PPy/GO composite agglomerates easily because of the dehydration of excess oxygen-containing groups on the GO sheets during the drying process. The dried PPy/rGO intermediate and its derived CNx/graphene products retain their high dispersion and loose-powder features. The as-prepared CNx/graphene composites have a total nitrogen content of about 10 at% and their nitrogen state is mainly of pyridinic and graphitic type. CNx/graphene composites exhibit excellent performance for the oxygen reduction reaction (ORR) in terms of electrocatalytic activity, stability and immunity towards methanol crossover and CO poisoning, suggesting their potential as metal-free electrocatalysts for the ORR.     

Carbon-nitrogen/graphene composite as metal-free electrocatalyst for the oxygen reduction reaction

Sheet-like carbon-nitrogen (CNx)/graphene composites with a high content of nitrogen (x≤0.15) was prepared by the carbonization of polypyrrole (PPy)/reduced-graphene-oxide (rGO) composite at 600-800°C. We used rGO instead of graphene oxide (GO) sheets as a template and a substrate to immobilize PPy since the PPy/GO composite agglomerates easily because of the dehydration of excess oxygen-containing groups on the GO sheets during the drying process. The dried PPy/rGO intermediate and its derived CNx/graphene...     

Nickel-introduced structurally ordered PtCuNi/C as high performance electrocatalyst for oxygen reduction reaction

Designing highly active and durable oxygen reduction reaction (ORR) electrocatalysts is essential for developing efficient proton-exchange membrane fuel cells (PEMFCs). In this work, ordered PtCuNi/C nanoparticles (NPs) were synthesized using an impregnation reduction method. This study shows that the incorporation of Ni in ordered PtCu/C can effectively adjust the electronic structure of Pt, thereby optimizing oxygen binding energy for the ORR. The obtained intermetallic ordered PtCuNi/C NPs significantly improved ORR activity and durability compared to ordered PtCu/C. Specifically, PtCu_0·5Ni_0·5/C-700 shows a mass activity of 1.29 ​A ​mg _Pt⁻¹ ​at 0.9 ​V vs. reversible hydrogen electrode (RHE), which is about 9.2 times higher than that of commercial Pt/C. PtCu_0.5Ni_0.5/C-700 is also shown to be competent cathode catalyst for a single-cell system exhibiting high power density (461 ​mW ​cm⁻²). This work demonstrates that ordered PtCu_0·5Ni_0·5/C-700 can be used as a highly active and durable ORR catalyst in PEMFCs.     

Vertically-interlaced NiFeP/MXene electrocatalyst with tunable electronic structure for high-efficiency oxygen evolution reaction

Layered double hydroxides (LDHs) with decent oxygen evolution reaction (OER) activity have been exten-sively studied in the fields of energy storage and convers...     

提升Pd基电催化剂氧还原活性的策略

氧还原反应(ORR)是许多电化学相关技术的核心反应,许多研究致力于制备同时具备高活性、高稳定性和低成本的催化剂.Pd基纳米材料由于其相对较优的催化性能和相对丰富的储量,有望成为Pt的替代品,受到了广泛关注,但要达到商品化程度,其性能需进一步提高.本文以Pd基催化剂应用于ORR电催化为背景,综述了近年来Pd基催化剂ORR...     

Central electron-enriched NO-FeN4 sites as superior acidic oxygen reduction reaction electrocatalysts for proton exchange membrane fuel cells

Developing nobel-metal-free catalysts, especially for iron-nitrogen on carbon (FeNC) materials, has been an urgent demand for wide applications of proton exchange membrane fuel cells (PEMFCs). However, the inferior oxygen reduction reaction (ORR) activity of traditional iron-nitrogen sites in acidic conditions seriously impedes the further improvement of their performance. Herein, we synthesized FeN₄ with NO (nitric oxide) group axial modification (denoted as NO-FeN₄) on a large scale through a confined small molecule synthesis strategy. Benefitting from the strong electron-withdrawing effect of the NO group, the central electron-rich FeN₄ site exhibits ultrahigh ORR activity with a three times higher mass activity (1.1 A·g?1 at 0.85 V) compared to the traditional FeN₄ sample, as well as full four-electron reaction selectivity. Moreover, the PEMFC assembled with the as-prepared electrocatalyst also exhibits a greatly enhanced peak power density (>725 mW·cm?2). This work provides a new approach to rationally design advanced M-N_x nonnoble electrocatalysts for the ORR.     

Nitrogen-doped graphene nanosheets as high efficient catalysts for oxygen reduction reaction

It is of great significance in exploring alternative catalysts to platinum (Pt)-based materials for oxygen reduction reaction (ORR),because this reaction is invariably involved in various fuel cells and metal-air batteries.We herein reported the nitrogen doped graphene nanosheets (NGNSs) with pore volume of as high as 3.42 m 3 /g and investigated their potential application as ORR catalysts,it was demonstrated the NGNSs featured high activity,improved kinetics and excellent long-term stability for ORR.The NGNSs were successfully used as cathode catalysts of microbial fuel cells (MFCs) and performed even better than the commercial Pt/C (Pt 10%) catalysts at the maximum power output.     

FeCo-based mesoporous carbon shells modified N-doped porous carbon spheres for oxygen reduction reaction

FeCo-based non-noble metal electrocatalysts (NNMEs) of FeCo/MCS-NPCS was fabricated by immobilization of hemin on mesoporous carbon shells modified N-doped porous carbon spheres (MCS-NPCS). The obtained FeCo/MCS-NPCS exhibits a half-wave potential (E_1/2) of 0.851 ​V versus the reversible hydrogen electrode (vs. RHE) and a limited-diffusion current density (J_L) of 5.45 ​mA ​cm⁻². In addition, FeCo/MCS-NPCS shows comparable oxygen reduction reaction (ORR) performances to 20 ​wt% Pt/C in terms of E_1/2 and J_L and better electrochemical properties, including the methanol tolerance and durability in alkaline solution. Such outstanding electrochemical activities of FeCo/MCS-NPCS can be ascribed to Fe and/or Co-based nitrides and carbides as well as N-doped carbon matrixes modified with mesoporous carbon shells. This research introduces a promising path to design and synthesize highly efficient FeCo–N–C electrocatalysts towards ORR.     

Surface modifications of Pt-based atomically ordered nanoparticles to improve catalytic performances for oxygen reduction reaction

Bimetallic platinum-cobalt (Pt–Co) nanostructure catalysts represent superior catalytic performances for oxygen reduction reaction (ORR). In a variety of Pt–Co catalyst structures, atomically ordered structure catalysts show excellent catalytic performances in the ORR. In this work, for promoting their catalytic performances, atomically ordered PtCo nanoparticles (PtCo/C) with carbon supported were successfully prepared by an improved impregnation method and annealing. Then, the ordered PtCo/C catalysts have been significantly improved by doped with ultralow amount of Au and Cr transition metal. The physical and electrochemical test results demonstrate the Cr–PtCo/C and Au–PtCo/C catalysts have superior catalytic performances including mass activity and stability compared to commercialized Johnson Matthey (JM) Pt/C, which was the result of the modified electronic properties of Pt surface and atomically ordered structure. The presence of Au and Cr enhances the stability of PtCo/C catalysts. This work represents a simple way to promote the catalytic performances of the atomically ordered catalysts.     

Photo-improved hydrogen evolution reaction activity of the Pt/CdS electrocatalyst

The effect of CdS content on the photo-induced improvement of hydrogen evolution reaction activity of the Pt/CdS electrocatalyst was investigated. Although the electrons transferred from CdS to Pt in the Pt/CdS electrocatalyst increased with the CdS content under illumination, the electrochemical active surface area of the Pt/CdS electrocatalyst decreased with the CdS content, resulting that the photo-induced improvement of hydrogen evolution reaction activity of the Pt/CdS electrocatalyst decreased with the CdS content.     

The synthesis and characterization of a Co-N/C composite catalyst for the oxygen reduction reaction in acidic solution

A non-precious metal Co-N/C catalyst for the oxygen reduction reaction (ORR) was synthesized by heating a mechanical mixture of cobalt chloride, urea and acetylene black under a nitrogen atmosphere. The catalyst was characterized by XRD and XPS. The electrocatalytic activity in the ORR was evaluated by linear sweep voltammetry in 0.5 mol L⁻¹ H₂SO₄ solution. The results show that the Co-N/C catalyst aids the reduction of oxygen. The presence of elemental cobalt in the precursor allows nitrogen atoms to embed themselves in the graphite matrix to form pyridinic and graphitic type C-N structures as the ORR active sites. The effect of heat-treating temperature on the catalytic activity was also investigated. The results also show that the Co-N/C catalyst is most active when pyrolyzed at 600°C. The obtained Co-N/C catalyst loses some activity after initial exposure to the H₂SO₄ solution because of leaching, but is then stable for up to 20 h immersion. The catalyst is also stable when charged, which is supported by the cyclic voltammetry results.     

气体扩散电极制备条件与氧还原反应活性关系的研究

在改变催化层中聚四氟乙烯(PTFE)、造孔剂含量和热压压力等条件下制备气体扩散电极,通过计时电位法、阴极极化曲线对气体扩散电极进行测定,并将其结果用最小二乘法拟合得出电极的制备条件与氧气还原反应电化学参数之间的关系。电化学测试结果表明,各种条件下制备的电极的阴极极化过程都符合Rho提出的半经验公式规律;当气体扩散电极催化层PTFE面密度3.33mg/cm²、造孔剂(NH₄)HCO₃面密度1.05mg/cm²以及热压压力3.69MPa时,气体扩散电极的氧还原活性最佳。     

热解聚苯胺合成氮掺杂MnCo2O4-C氧还原催化剂

通过热解聚苯胺涂层的Mn Co2O4颗粒制备出Mn Co2O4/N-C材料,即一种新型的碱性聚合物电解质膜燃料电池(APEFC)阴极非贵金属催化剂。在不同温度下热处理得到了一系列的Mn Co2O4/N-C催化剂,对其进行XRD、Raman、XPS表征和LSV电化学测试,结果表明:热处理温度为900℃,Mn Co2O4质量分数为15%时,Mn Co2O4/N-C催化剂具有最佳的催化活性,氧还原反应起始电位为0.90 V;该催化剂中石墨型的碳和氮含量最高,这是其具有较高的氧还原催化活性一个重要因素。     

氮掺杂石墨烯凝胶的制备及其氧还原催化性能

以氧化石墨烯为原料,采用水热法合成出具有三维网络结构的氧化石墨烯凝胶,并与氨气在高温下反应制得具有三维多孔结构的氮掺杂石墨烯凝胶(N-G-F)。通过SEM、TEM、BET、XPS等分析手段对N-G-F的形貌结构及组成进行了系统表征,使用旋转圆盘电极测试了其对氧还原反应的催化活性。结果表明,N-G-F的氧还原反应具有高起始电位(-0.1 V)、四电子转移的反应特征和高的动力学电流密度(9.1 m A/cm2),高于商业化Pt-C的电催化性能。     

二氧化锰/多壁碳纳米管复合材料对氧还原(ORR)催化作用的初步研究

用循环伏安方法制备了二氧化锰／多壁碳纳米管（MnO2／MwCNTs）复合材料,分别在中性和弱碱性的硫酸钠溶液中对其进行氧还原电化学测试。结果显示,在合适条件下,MnO2／MwCNTs复合材料的电催化还原氧气的电流值明显大于单独MWCNTs和单独MnO2电催化还原电流值,说明MnO2／MWCNTs复合材料具有良好的催化还原活性;在弱碱性的环境下,随着碱性的增强,MnO2／MWCNTs复合材料的电催化还原活性逐渐增强,同时显示出稳定的电催化还原～活性。     

查耳酮衍生物与丙二酸二酯的不对称迈克尔加成反应研究

查尔酮或带有查尔酮片段的衍生物具有抗炎症、抗细菌、除草等功效.以(R)-ALB为催化剂,叔丁醇钾作碱源,通过不对称迈克尔加成反应合成了一系列具有光学活性查耳酮片段的1,5-二羰基化合物,并且取得了良好的产率和极高的对映选择性.反应收率最高可达84%,反应的对映选择性最高可达98%.     

Grain size effect of IrO2 nanocatalysts for the oxygen evolution reaction

Combined with air annealing, rutile-structured IrO 2 nanoparticles with various sizes were prepared using colloidal method. The nanoparticles were used as the electrocatalysts for the oxygen evolution reaction (OER) in acidic media, and their grain size effect was studied. The results show that with the increase in annealing temperature, the grain size of the catalyst increases, and the voltammetric charges (the electroactive areas) and apparent activity for the OER decrease. The relationship between the intrinsic activity and the annealing temperature exhibits a volcano-type curve and the catalyst annealed at 550 ℃ achieved the best result.