Preparation of high active Pt/C cathode electrocatalyst for direct methanol fuel cell by citrate-stabilized method

Platinum nanoparticles supported on carbons（Pt/C,60%,mass fraction） electrocatalysts for direct methanol fuel cell（DMFC） were prepared by citrate-stabilized method with different reductants and carbon supports.The catalysts were characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM） and cyclic voltammetry（CV）.It is found that the size of Pt nanoparticles on carbon is controllable by citrate addition and reductant optimization,and the form of carbon support has a great influence on electrocatalytic activity of catalysts.The citrate-stabilized Pt nanoparticles supported on BP2000 carbon,which was reduced by formaldehyde,exhibit the best performance with about 2 nm in diameter and 66.46 m2/g（Pt） in electrocatalytic active surface（EAS） area.Test on single DMFC with 60%（mass fraction） Pt/BP2000 as cathode electrocatalyst showed maximum power density at 78.8 mW/cm2.

由2.5-二甲氧基氯苯合成4-氯-2.5-二甲氧基苯胺研究

本文对由2.5-二甲氧基氯苯合成4-氯-2.5-二甲氧基苯胺的过程进行了实验、研究,通过对比,确定了投料配比、辅助催化剂、硝化和还原工艺路线。

A Layer-Structured Metal-Organic Framework-Derived Mesoporous Carbon for Efficient Oxygen Reduction Reaction

Developing highly active and durable electrocatalysts for the oxygen reduction reaction （ORR） is crucial to large-scale commercialization of fuel cells and metal-air batteries. Here we report a facile approach for the synthesis of nitrogen and oxygen dual-doped meso-porous layer-structured carbon electrocatalyst embedded with graphitic carbon coated cobalt nanoparticles by direct pyrolysis of a layer-structured metal-organic framework. The elec- trocatalyst prepared at 800℃ exhibits comparable ORR performance to Pt/C catalysts but possesses superior stability to Pt/C catalysts. This synthetic approach provides new prospects in developing sustainable carbon-based electrocatalysts for electrochemical energy conversion devices.

Interface-controlled synthesis of CeO_2(111) and CeO_2(100) and their structural transition on Pt(111)

Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surface structures is required.We have thus studied the growth of CeOx nanostructures(NSs)and thin films on Pt(111).The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts.However,the Pt-CeOx interaction has not been understood at the atomic level.We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria,which could subsequently determine their catalytic chemistry.While ceria on Pt(111)typically exposes the CeO2(111)surface,we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures,owing to the electronic interaction between Pt and CeOx.A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111)substrate.For a ceria film of^3–4 monolayer(ML)thickness on Pt(111),annealing in ultrahigh vacuum(UHV)at 1000 K results in a surface of CeO2(100),stabilized by a c-Ce2O3(100)buffer layer.Further oxidation at 900 K transforms the surface of the CeO2(100)thin film into a hexagonal CeO2(111)surface.

Three-dimensional porous superaerophobic nickel nanoflower electrodes for high-performance hydrazine oxidation

Finding inexpensive electrodes with high activity and stability is key to realize the practical application of fuel cells. Here, we report the fabrication of three-dimensional （3D） porous nickel nanoflower （3D-PNNF） electrodes via an in situ reduction method. The 3D-PNNF electrodes have a high surface area, show tight binding to the electroconductive substrate, and most importantly, have superaerophobic （bubble repellent） surfaces. Therefore, the electrocatalytic hydrazine oxidation performance of the 3D-PNNF electrodes was much higher than that of commercial Pt/C catalysts because of its ultra-weak gas-bubble adhesion and ultra-fast gas-bubble release. Furthermore, the 3D-PNNF electrodes showed ultra-high stability even under a high current density （260 mA/cm^2）, which makes it promising for practical applications. In addition, the construction of superaerophobic nanostructures could also be beneficial for other gas evolution processes （e.g., hydrogen evolution reaction）.

Conversion of bimetallic MOF to Ru-doped Cu electrocatalysts for efficient hydrogen evolution in alkaline media

The rational design and construction of inexpensive and highly active electrocatalysts for hydrogen evolution reaction(HER)is of great importance for water splitting.Herein,we develop a facile approach for preparation of porous carbon-confined Ru-doped Cu nanoparticles(denoted as Ru-Cu@C)by direct pyrolysis of the Ru-exchanged Cu-BTC metal–organic framework.When served as the electrocatalyst for HER,strikingly,the obtained Ru-Cu@C catalyst exhibits an ultralow overpotential(only 20 mV at 10 mA cm^(-2))with a small Tafel slope of 37 m V dec^(-1)in alkaline electrolyte.The excellent performance is comparable or even superior to that of commercial Pt/C catalyst.Density functional theory(DFT)calculations confirm that introducing Ru atoms into Cu nanocrystals can significantly alter the desorption of H_(2) to achieve a close-to-zero hydrogen adsorption energy and thereby boost the HER process.This strategy gives a fresh impetus to explore low-cost and high-performance catalysts for HER in alkaline media.

A bio-inspired Co304-polypyrrole-graphene complex as an efficient oxygen reduction catalyst in one-step ball milling

The development of non-precious metal-based electrocatalysts has attracted much research attention because of their high oxygen reduction reaction （ORR） activities, low cost, and good durability. By one-step in-situ ball milling of graphite, pyrrole, and cobalt salt without resorting to high-temperature annealing, we developed a general and facile strategy to synthesize bio-inspired cobalt oxide and polypyrrole coupled with a graphene nanosheet （Co3O4-PPy/GN） complex. Herein, the exfoliation of graphite and polymerization of pyrrole occurred simultaneously during the ball milling process. Meanwhile, the Co3O4 and Co-Nx ORR active sites were generated from the oxidized cobalt ion, cobalt-PPy, and the newly exfoliated graphene nanosheets via strong π-π stacking interactions. The resultant Co3O4-PPy/GN catalysts showed efficient electrocatalytic performances for ORRs in an alkaline medium with a positive onset and reduction potentials of -0.102 and -0.196 V （vs. Ag/AgCl）, as well as a high diffusion-limited current density （4.471 mA·cm^-2）, which was comparable to that of a Pt/C catalyst （4.941 mA·cm^-2）. Compared to Pt/C, Co3O4-PPy/GN catalysts displayed better long-term stability, methanol tolerance, and anti-CO-poisoning effects, which are of great significance for the design and development of advanced non-precious metal electrocatalysts.

Coprinus comatus-derived nitrogen-containing biocarbon electrocatalyst with the addition of self-generating graphene-like support for superior oxygen reduction reaction

The development of nitrogen-rich biomass- derived carbon catalysts provides an attractive perspective to substitute for Pt-based electrocatalysts for oxygen reduction reaction （ORR）. We here report a facile strategy for synthesis of a nitrogen-doped biocarbon/graphene-like composite electrocatalyst by pyrolyzing a solid-state mixture of coprinus comatus biomass and melamine under nitrogen protection. The graphtic carbon nitride formed by polycondensation of melamine at 600 ℃ acts as a self-sacrificing template to generate the nitrogen-doped graphene-like sheet, which can function as an inserting agent and self-generating support. The composite catalyst exhibits the most promising catalytic activity towards the four-electron ORR with a half-wave potential of around 0.83 V （vs. RHE）, and more excellent stability and tolerance to methanol/ethanol compared to the commercial Pt/C catalyst. It is interestingly found that both a higher content of nitrogen and a larger ratio of graphitic-nitrogen species, which may derive from self-addition of graphene-like support into the catalyst, can effectively improve theelectrocatalytic activity. The planar N group may be the nitrogen functionality that is most responsible for main-taining the ORR activity in alkaline medium. This study can largely encourage the exploration of high-performance carbon-based catalysts from economical and sustainable fungus biomass.

Highly dispersed L1_(0)-PtZn intermetallic catalyst for efficient oxygen reduction

Highly active and durable electrocatalysts with minimal Pt usage are desired for commercial fuel cell applications.Herein,we present a highly dispersed L1_(0)-PtZn intermetallic catalyst for the oxygen reduction reaction(ORR),in which a Zn-rich metal–organic framework(MOF)is used as an in situ generated support to confine the growth of PtZn particles.Despite requiring high-temperature treatment,the intermetallic L1_(0)-PtZn particles exhibit a small mean size of3.95 nm,which confers the catalysts with high electrochemical active surface area(81.9 m^(2)g_(Pt)^(-1))and atomic utilization.The Pt electron structure and binding strength between Pt and oxygen intermediates are optimized through ligand effect and compressive strain.These advantages result in ORR mass activity and specific activity of 0.926 A mg_(Pt)^(-1) and 1.13 mA cm^(-2),respectively,which are 5.4 and 4.0 times those of commercial Pt/C.The stable L10structure provides the catalysts with superb durability;only a halfwave potential loss of 11 mV is observed after 30,000 cycles of accelerated stress tests,through which the structure evolves into a more stable PtZn-Pt core-shell structure.Therefore,the development of a Zn-based MOF as a catalyst support is demonstrated,providing a synergy strategy to prepare highly dispersed intermetallic alloys with high activity and durability.

Nanomagnetic CoPt truncated octahedrons:facile synthesis,superior electrocatalytic activity and stability for methanol oxidation

Nanomagnetic CoPt truncated octahedral nanoparticles （TONPs） were successfully synthesised through a facile one-pot strategy. These single crystal CoPt TONPs with an average size of about 8 nm exhibit excellent electrocatalytic performance of both activity and stability for methanol oxidation reaction （MOR）. The mass and specific activities of CoPt TONPs is 8 and 6 times higher than that of standard commercial Pt/C, respectively. After accelerated durability test （ADT）, the loss of electrochemical surface area （ECSA） for CoPt TONPs is only 18.5%, which is significantly less than that of commercial Pt/C （68.2%）, indicating that CoPt TONPs possess much better stability than commercial Pt/C in the prolonged operation. The Curie temperature of CoPt TONPs down to 8 nm is as high as 350 K with weak ferromagntism at room temperature （RT）, which is greatly valuable for recycling in the eletrocatalytic applications.

Octahedral PtNi nanoparticles with controlled surface structure and composition for oxygen reduction reaction

Controlling the surface structure and composi- tion at the atomic level is an effective way to tune the cat- alytic properties of bimetallic catalysts. Herein, we demon- strate a generalized strategy to synthesize highly monodis- perse, surfactant-free octahedral PtxNi1-x nanoparticles with tunable surface structure and composition. With increasing the Ni content in the bulk composition, the degree of concave- ness of the octahedral PtxNi1-x nanoparticles increases. We systematically studied the correlation between their surface structure/composition and their observed oxygen reduction activity. Electrochemical studies have shown that all the octa- hedral PtxNi1-x nanoparticles exhibit enhanced oxygen reduc- tion activity relative to the state-of-the-art commercial Pt/C catalyst. More importantly, we find that the surface struc- ture and composition of the octahedral PtxNi1-x nanoparti- cles have significant effect on their oxygen reduction activ- ity. Among the studied PtxNi1-x nanoparticles, the octahedral PtlNi1 nauoparticles with slight concaveness in its （111） facet show the highest activity. At 0.90 V vs. RHE, the Pt mass and specific activity of the octahedral PhNil nanoparticles are 7.0 and 7.5-fold higher than that of commercial Pt/C catalyst, re- spectively. The present work not only provides a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral PtxNi1-x nanoparticles with tunable surface struc- ture and composition, but also provides insights to the struc- ture-activity correlation.

Pt/Zn heterostructure as efficient air-electrocatalyst for long-life neutral Zn-air batteries

Neutral Zn-air batteries(ZABs) have attracted much attention due to the enhanced lifespan and stability.However, their development is suppressed by the poor catalytic properties of the air-electrocatalysts for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). Hence,the exploration of highly efficient electrocatalysts for neutral ZABs is critical. Herein, we designed an economical heterostructure of Pt nanoparticle-modified Zn nanoplates(Pt/Zn NPs). Compared with commercial Pt/C electrocatalyst, our Pt/Zn heterostructure exhibits comparable catalytic properties and ultrahigh stability in neutral media. The heterostructure can reduce the dosage of Pt and offer sufficient active sites,resulting in enhanced catalytic properties for ORR/OER in neutral media. When applied to neutral ZABs as air cathode,our heterostructure exhibits a high power density of 45 mW cm^(-2) and excellent stability of more than 850 cycles with negligible decay, making it the most efficient and robust one in neutral electrolyte. This approach opens a new avenue to strategically design catalysts with high activity for neutral ZABs, rendering them potential in portable and wearable electronic devices.

Mass production of high-performance single atomic FeNC electrocatalysts via sequenced ultrasonic atomization and pyrolysis process

Mass production of highly efficient,durable,and inexpensive single atomic catalysts is currently the major challenge associated with the oxygen reduction reaction(ORR)for fuel cells.In this study,we develop a general strategy that uses a simple ultrasonic atomization coupling with pyrolysis and calcination process to synthesize single atomic FeNC catalysts(FeNC SACs)at large scale.The microstructure characterizations confirm that the active centers root in the single atomic Fe sites chelating to the four-fold pyridinic N atoms.The identified specific Fe active sites with the variable valence states facilitate the transfer of electrons,endowing the FeNC SACs with excellent electrochemical ORR activity.The FeNC SACs were used as cathode catalysts in a homemade Zn-air battery,giving an open-circuit voltage(OCV)of 1.43 V,which is substantially higher than that of commercial Pt/C catalysts.This study provides a simple approach to the synthesis of single atomic catalysts at large scale.

Fine decoration of carbon nanotubes with metal organic frameworks for enhanced performance in supercapacitance and oxygen reduction reaction

Efficient electrode material is crucial for energy conversion from renewable sources such as solar electricity. We present a method for preparation of carbon nanotubes （CNTs） with zeolitic imidazolate frameworks （ZIFs, e.g., ZIF-8） via an in situ pyrolysis process. The resultant materials are completely new carbon composites with desirable hierarchical porosity and nitrogen-doped features. Electron microscopy images show that CNTs with small external diameters enable more uniform dispersion of ZlF-8-derived carbons, subsequently yielding a unique hierarchically porous structure. Such carbon shows superior activity in oxygen reduction reaction （ORR） and high performance of supercapacitance, making it a valu- able metal-flee electrode material and a competent alternative to the state-of-the-art Pt/C catalyst. The electrocatalytic performance of CNTs can be dramatically improved by the incorporation of ZIF-8-derived carbons, which is attributed to the combination of good conductivity, abundant accessible dopant species, as well as proper porosity. Our method offers a new avenue for constructing electrocatalysts by effective integration of ZlF-8-derived carbon and the CNTs skeleton.

Insight on the active sites of CoNi alloy embedded in N-doped carbon nanotubes for oxygen reduction reaction

Transition metal alloy electrocatalysts have sparked intense interest for their use in oxygen reduction reaction(ORR).However,there is almost no corresponding research on the alloy active sites.In this study,CoNi alloy nanoparticles embedded in bamboo-like N-doped carbon nanotubes(CoNi-NCTs)as catalysts constructed by a facile pyrolysis of Prussian blue analogs were investigated.The density functional theory calculation reveals that the oxygen molecules are more easily adsorbed on the Ni sites in these catalysts,while the Co sites favor the formation of OOH★intermediates during ORR.In addition,the cooperation of the CoNi alloys with the N-doped carbon benefits electron transfer and promotes electrocatalytic activity.The optimized CoNi-NCT shows remarkable ORR catalytic activity with an half-wave potential(E1/2)of 0.83 V,an onset potential(Eonset)of 0.97 V,and superior durability,all of which surpass the commercial Pt/C catalysts.The assembled zinc-air battery delivers a small charge/discharge voltage gap of 0.86 V at 10 mA cm^(-2),a high-power density of 167 mW cm^(-2),and good stability(running stably over 900 cycles).

Shape-controlled Pt nanocubes directly grown on carbon supports and their electrocatalytic activity toward methanol oxidation

Synthesis of shape-controlled Pt nanocrystals is substantial and important for enhancing chemical and electrochemical reactions.However,the removal of capping agents,shape-controlling chemicals,on Pt surfaces is essential prior to conducting the catalytic reactions.Here we report a facile one-pot synthesis of Pt nanocubes directly grown on carbon supports(Pt nanocubes/C) with modulating the kinetic reaction factors for shaping the nanocrystals,but without adding any capping agents for preserving the clean Pt surfaces.Well-dispersed Pt nanocubes/C shows enhanced activity and long-term stability toward methanol oxidation reaction compared to the commercial Pt/C catalyst.

Highly dispersed Pt species anchored on W_(18)O_(49)nanowires mediate efficient and durable hydrogen evolution in acidic water

Platinum-based material is the most efficient and durable electrocatalyst for motivating the hydrogen evolution reaction(HER)in an acidic electrolyte;however,its low abundance and high cost limit its further application in proton-exchange membrane water electrolysis(PEMWE)technology.Therefore,minimizing the Pt amount while retaining high activity would be desirable.Herein,we use defect-rich W_(18)O_(49)nanowires to anchor well-dispersed,ultrafine Pt species(Pt-W_(18)O_(49))via a freeze-drying method to avoid aggregation,further mediating an efficient and durable HER in acidic water.Density functional theory analyses also demonstrate that the strong electronic interaction between the Pt species and W_(18)O_(49)support greatly improves the HER performance.With a 1/10 Pt loading amount of the commercial 20 wt%Pt/C,the Pt-W_(18)O_(49)catalyst requires the overpotentials of 116 and 743 mV to achieve high current densities of 100 and 1000 mA cm^(−2)in 0.5 mol L^(−1)H_(2)SO_(4),outperforming those of the 20 wt%Pt/C benchmark.More importantly,the Pt-W_(18)O_(49)catalyst can sustain a high-currentdensity HER at 500 mA cm^(−2)for more than 38 h without obvious degradation.This work paves a new avenue for synergistically reducing the Pt amount and retaining high activity for real-world PEMWE.

Multimetallic AuPd@Pd@Pt core-interlayer-shell icosahedral electrocatalysts for highly efficient oxygen reduction reaction

Incorporating Pt with core metals into Pt-based core-shell catalysts is regarded as a promising strategy to substantially enhance the catalytic properties towards oxygen reduction reaction(ORR) in fuel cells due to the synergetic effect between distinct metals. In this wok, ultrathin Pt skins with two atomic layers were epitaxially coated on as-prepared icosahedral Au_50Pd_50, Au_60Pd_40 and Au_66Pd_34 nanocrystal seeds,which are constructed with alloyed cores and Pd shells with different thickness. Through electron microscopic characterizations, Pd interlayers with tunable thickness of 3, 6, and 12 atomic layers can be found in the Au_66Pd_34@Pt, Au_60 Pd_40@Pt and Au_50Pd_50@Pt icosahedra, respectively. These icosahedral Au Pd@Pd@Pt nanocrystals show substantially enhanced activities and durabilities in electrocatalytic measurements towards ORR compared to Au_75Pd_25@Pt icosahedra without Pd interlayer and commercial Pt/C catalysts. Specifically, Au_60Pd_40@Pt icosahedra with 6 atomically thick Pd interlayer display the best electrocatalytic performances, whose mass activities before and after durability tests of 50,000 cycles are11.6 and 30.2 times, respectively, as high as that of the commercial Pt/C.

Size effects of platinum particles@CNT on HER and ORR performance

Platinum(Pt)is an efficient catalyst for hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR),but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist.The strong metal–support interaction(SMSI)between the metal and carrier causes the charge transfer and mass transport from the support to the metal.Herein,Pt species(0.5 wt.%)with various particle sizes supported on carbon nanotubes(CNTs)have been synthesized by a photo-reduction method.The^1.5 nm-sized Pt catalyst shows much higher HER performance than the counterparts in all pH solutions,and the mass activity of it is even 23–36 times that of Pt/C.While for ORR,the^3 nm-sized Pt catalyst exhibits the optimal performance,and the mass activity is 3 times and even 16 times that of Pt/C in acidic and alkaline media,respectively.The high HER and ORR performances of the^1.5 nm-and^3 nm-sized Pt catalysts benefit from the SMSI between Pt and the CNTs matrix and the higher ratio of face sites to edge sites,which is meaningful for the design of efficient electrocatalysts for renewable energy application.

Interface engineering of snow-like Ru/RuO2 nanosheets for boosting hydrogen electrocatalysis

Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless, the quest of high-efficiency Ru-based catalysts for HOR and HER is driven by the current disadvantages including low activity and unsatisfactory stability. Herein, we have fabricated and engineered two-dimensional(2D) Ru-based snow-like nanosheets with Ru/Ru O2interface(Ru/Ru O2SNSs)via a post-annealing treatment. Detailed characterizations and theoretical calculations indicate that the interfacial synergy, which is dependent on the temperature for annealing, can alter the hydrogen binding energy(HBE) and hydroxide binding energy(OHBE), as a result of the enhanced HOR and HER performance. Impressively, the optimal Ru/RuO_(2) SNSs display a mass activity of 9.13 A mgRu^(–1) at an overpotential of 50 m V in 0.1 mol L^(–1) KOH for HOR, which is 65, 304, and 21 times higher than those of Ru SNSs(0.14 A mg_(Ru)^(–1)), RuO_(2) SNSs(0.03 A mg_(Ru)^(–1)), and commercial Pt/C(0.43 A mg_(Ru)^(–1)), respectively.Moreover, Ru/RuO_(2) SNSs display improved HER activity with a low overpotential of 20.2 m V for achieving10 m A cm^(-2)in 1 mol L^(–1)KOH. This work not only provides an efficient catalyst for HOR and HER, but also promotes fundamental research on the fabrication and modification of catalysts in heterogeneous catalysis.