Carbon-supported Nanoparticles Research Articles

Investigating the pH-Dependent Activity, Selectivity, and Dynamics of Metal Nitride Electrocatalysts for Fuel Cells and Electrolyzers

To mitigate climate change caused by the use of fossil fuel energy sources, there is an urgent need to decarbonize our energy systems. Developing fuel cell and water electrolysis technologies to support a green hydrogen infrastructure is a promising strategy for this transition. In both hydrogen fuel cells and water electrolyzers, platinum-group metal (PGM) materials such as Pt and IrOx are benchmark electrocatalysts, exhibiting high activity and stability for kinetically-hindered reactions including the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER), and alcohol oxidation reactions (AOR; alternative anodic reactions to OER). Despite their remarkable performance, the high cost and low abundance of PGMs is a key factor limiting the widespread adoption of these technologies.Cobalt- and nickel-based metal and oxide catalysts have emerged in the literature as a promising PGM-alternative class of low-cost, high-performing ORR, OER and AOR catalysts. Substituting oxides with nitrides or other chalcogenides could be a favorable method to improve activity, selectivity, and stability; however, the material stability of these non-oxides as a function of reaction, potential window, and pH is not well-understood. Furthermore, the most active of these materials tend to be carbon-supported nanoparticles with complicated and heterogeneous active sites, which makes deconvoluting the role of the cobalt and secondary element(s) (e.g. N, C, etc.) difficult.With the goal of developing fundamental activity-stability relationships for non-precious metal-based electrocatalysts, we have developed a synthesis procedure for well-defined Co- and Ni-based thin film materials. Focusing on Co, using physical vapor deposition followed by thermal treatments with ammonia and an Sb-based precursor, we have synthesized CoxSbyNz thin films of varying compositions. These synthesis methods can be extended to synthesize a broad class of metallic (Co, Ni, Fe, etc.) or bimetallic X-ide (X = N, S, etc.) thin film materials. We evaluate ORR, OER, and AOR activity with cyclic voltammetry, demonstrating that activity depends on composition and electrolyte pH. Specifically, for Co-based thin films for ORR, we see improvement in activity with the incorporation of N, and improvement in acid-stability with the incorporation of Sb. In addition to ex situ post-characterization with x-ray photoelectron spectroscopy, we utilize in situ techniques to evaluate catalyst stability in real time. We monitor time- and potential-dependent cobalt dissolution with an on-line inductively coupled plasma mass spectrometer (ICP-MS) as well as nitride degradation with electrochemical mass spectrometry (EC-MS). In acidic media, the stability of CoxN is limited by Co dissolution, while in alkaline media stability appears to be limited by nitride degradation. With highly active non-oxide materials it is typically too complicated to disentangle the role of each individual element within an electrocatalyst. With our stepwise material synthesis platform and multifaceted characterization techniques we are able to individually probe the material stability and product-specific activity of each element. These results provide new insights to guide the strategic design of electrocatalysts across a range of reactions and applications.

Stability of Carbon-Supported Nanoparticles in Hydrogen Fuel Cells Resolved by Automated Electron Tomography

Stability of Carbon-Supported Nanoparticles in Hydrogen Fuel Cells Resolved by Automated Electron Tomography

Exploring the impact of partial pressure and typical compounds on the continuous electroconversion of CO2 into formate

Previous research in CO2 electroreduction primarily focused on cathodic electrocatalysts and electrode configurations using pure CO2. Few studies explored the impact of residence time and N2/O2 compounds, crucial for practical industrial implementation. In this study, the effect of residence time and the influence of N2 and O2 compounds on CO2 electroreduction to formate are investigated, employing Bi carbon-supported nanoparticles in the form of Gas Diffusion Electrodes within an electrochemical flow reactor with a single pass of the reactants. The results highlight the critical role of residence time and the impact of N2 and O2 compounds in the CO2 electroconversion process. On the one hand, the evaluation of residence time holds paramount significance for the potential establishment of a large-scale CO2 recycling plant, as it has the potential to significantly impact both the capital and operational costs of the integrated electrolyzer-separator system. Optimal results are obtained in the range of residence times between 1.8 and 2.9 seconds, corresponding to CO2 flow rates of 150 and 250 mL·min−1, respectively. On the other hand, the study resulted in a promising Faradaic Efficiency for formate of 75.0%, with similar values achieved at CO2 concentrations in the range of 75 – 100 vol%. These results are particularly noteworthy as they demonstrate that achieving a CO2 capture efficiency of 100% is not necessary, thereby reducing the costs associated with this process and, consequently, the overall cost of integrating both capture and utilization processes in a CO2 recycling plant.

Stability of high-entropy alloys under electrocatalytic conditions

High-entropy alloys are claimed to possess superior stability due to thermodynamic contributions. However, this statement mostly lies on a hypothetical basis. In this study, we use on-line inductively coupled plasma mass spectrometer to investigate the dissolution of five representative electrocatalysts in acidic and alkaline media and a wide potential window targeting the most important applications. To address both model and applied systems, we synthesized thin films and carbon-supported nanoparticles ranging from an elemental (Pt) sample to binary (PtRu), ternary (PtRuIr), quaternary (PtRuIrRh), and quinary (PtRuIrRhPd) alloy samples. For certain metals in the high-entropy alloy under alkaline conditions, lower dissolution was observed. Still, the improvement was not striking and can be rather explained by the lowered concentration of elements in the multinary alloys instead of the synergistic effects of thermodynamics. We postulate that this is because of dissolution kinetic effects, which are always present under electrocatalytic conditions, overcompensating thermodynamic contributions.

Transient and general synthesis of high-density and ultrasmall nanoparticles on two-dimensional porous carbon via coordinated carbothermal shock

Carbon-supported nanoparticles are indispensable to enabling new energy technologies such as metal-air batteries and catalytic water splitting. However, achieving ultrasmall and high-density nanoparticles (optimal catalysts) faces fundamental challenges of their strong tendency toward coarsening and agglomeration. Herein, we report a general and efficient synthesis of high-density and ultrasmall nanoparticles uniformly dispersed on two-dimensional porous carbon. This is achieved through direct carbothermal shock pyrolysis of metal-ligand precursors in just ~100 ms, the fastest among reported syntheses. Our results show that the in situ metal-ligand coordination (e.g., N → Co2+) and local ordering during millisecond-scale pyrolysis play a crucial role in kinetically dominated fabrication and stabilization of high-density nanoparticles on two-dimensional porous carbon films. The as-obtained samples exhibit excellent activity and stability as bifunctional catalysts in oxygen redox reactions. Considering the huge flexibility in coordinated precursors design, diversified single and multielement nanoparticles (M = Fe, Co, Ni, Cu, Cr, Mn, Ag, etc) were generally fabricated, even in systems well beyond traditional crystalline coordination chemistry. Our method allows for the transient and general synthesis of well-dispersed nanoparticles with great simplicity and versatility for various application schemes.

Isopropanol electro-oxidation on Pt-Ru-Ir: A journey from model thin-film libraries towards real electrocatalysts

Liquid fuels are considered a promising alternative to hydrogen in proton exchange membrane fuel cells. In particular, isopropanol, which can be selectively oxidised to acetone and further hydrogenated back to isopropanol using electrochemical and heterogeneous catalysis routes, respectively, opens the possibility of zero-emission fuel cell operation without complex management of molecular H2. However, the maximum electric power of such fuel cells is still relatively low, which is attributed to the poisoning of state-of-the-art Pt-Ru electrocatalysts by adsorbed acetone and/or Ru oxide/hydroxide. Here, in order to mitigate Pt-Ru poisoning at higher anodic potentials during isopropanol oxidation in acidic media, the effect of the addition of Ir, a less oxophilic element than Ru, on the activity and stability during dynamic experiments of Pt-Ru is systematically investigated. To identify the most active compositions, Pt-Ru-Ir thin-film material libraries are prepared using magnetron co-sputtering. The electrocatalytic activity of the libraries is screened using a high-throughput scanning flow cell setup. Catalysts with the highest activity are further synthesised in the form of carbon-supported nanoparticles. Comparing the two systems, similar trends are observed, highlighting the model material libraries being an excellent starting point for novel catalyst development. Besides electrocatalytic activity, catalyst shelf-life and dissolution stability are studied. While significant ageing in the air is found, partial reactivation is possible using a reductive treatment. The dissolution of the most promising nanoparticulate electrocatalyst is evaluated using online inductively coupled plasma mass spectrometry to assess the effect of Ir addition on Pt and Ru stability. No significant stabilising role of Ir, however, is observed. Hence, further optimisation of Pt-Ru or Pt-Ru-Ir is still needed to improve isopropanol fuel cell performance.

Tracking the Mn Diffusion in the Carbon-Supported Nanoparticles Through the Collaborative Analysis of Atom Probe and Evaporation Simulation.

Carbon-supported nanoparticles have been used widely as efficient catalysts due to their enhanced surface-to-volume ratio. To investigate their structure–property relationships, acquiring 3D elemental distribution is required. Here, carbon-supported Pt, PtMn alloy, and ordered Pt3Mn nanoparticles are synthesized and analyzed with atom probe tomography as model systems. A significant difference of Mn distribution after the heat-treatment was found. Finally, the field evaporation behavior of the carbon support was discussed and each acquired reconstruction was compared with computational results from an evaporation simulation. This paper provides a guideline for studies using atom probe tomography on the heterogeneous carbon-supported nanoparticle system that leads to insights toward a wide variety of applications.

Tailoring the Durability of Carbon-Coated Pd Catalysts Towards Hydrogen Oxidation Reaction (HOR) in Alkaline Media

For the hydrogen oxidation reaction (HOR), platinum group metal (PGM) catalysts are still the norm, and their large initial catalytic activity is counterbalanced by their uncertain durability in alkaline environments: harsh degradations proceed, like detachment and agglomeration of metallic nanoparticles from the carbon support, as witnessed from dedicated accelerated stress tests (AST). Herein, a strategy to increase such catalysts’ durability is provided, using carbon layers surrounding the Pd-based carbon-supported nanoparticles. The robustness of such catalysts, baring 0.5- or 0.7-nm-thick carbon cap over the Pd nanoparticles, is evaluated from AST combined with several pre/post-test characterization techniques: identical location transmission electron microscopy (IL-TEM), ex situ X-ray photoelectron spectroscopy (XPS) and ex situ inductively coupled plasma mass spectrometry (ICP-MS). The carbon layer protection limits the Pd-based nanoparticles’ agglomeration, detachment, and metal leaching, improving long-term catalyst durability in HOR-like operation. Thicker carbon layers surrounding the Pd nanoparticles lead to higher materials durability and lower degradation rate (larger performance stability) upon AST, compared to thinner carbon layers. In addition, the carbon-capped catalysts enable to maintain better the required Pd/PdO state of the surface that is essential for fast HOR, resulting in superior intrinsic HOR activity versus unprotected Pd/C. Overall, this work demonstrates that the activity-durability relationship can be tuned for carbon-capped catalysts.Graphical Abstract

Catalyst Development for the Electrochemical Oxidation of Isopropanol in LOHC Fuel Cells

The transportation sector is certainly one of the largest contributors to energy consumption worldwide and its further growth is still expected. To keep up with this huge energy demand from the mobility, it is inevitable for the whole sector to undergo the transition towards renewable energy resources as soon as possible. There are several approaches that can be considered; as in fuel cell research, hydrogen fuel cells are the most studied, and current focus lies on optimization of different parts starting from the actual catalytic material towards the whole engineering design to increase their efficiency. The current infrastructure for liquid fuels cannot be used for hydrogen and its long-term storage is problematic due to safety concerns. An alternative could be the use of a liquid fuel possessing the benefits of hydrogen oxidation such as high selectivity and comparably fast oxidation, simultaneously tackling the mentioned disadvantages. The electrocatalytic oxidation of isopropanol on PtRu offers a viable solution due to its low overpotential and nearly 100 % selectivity towards acetone under fuel cell operation conditions.1 This opens the possibility of the zero-emission operation of the fuel cell where the formed acetone can be recycled to isopropanol when the fuel cell is coupled to a transfer hydrogenation unit. 1 Still, there are several challenges yet to be overcome : first, restricting only to the catalyst, PtRu-based materials seem to be the most promising due to the oxidation of isopropanol at low overpotentials attributed to Pt-Ru sites.1, 2 However, PtRu itself suffers from surface poisoning by acetone leading to a gradual loss of activity3. Therefore, to overcome these limitations there is an urgent need to develop new materials or explore modified electrocatalyst surfaces that could lead to improved direct isopropanol fuel cell (DIFC) efficiencies.In this work, we present our recent findings on catalyst development for the electrochemical oxidation of isopropanol. Firstly, the electrocatalytic activity towards isopropanol oxidation of PtRu-based, ternary alloys was studied where the Pt:Ru:X (X= Ir, Au, Ni, Cu, Co, Mo, Ti, Pd) ratio was fixed to 45:45:10 at%. Among these, PtRuIr proven to be the best-performing candidate. As a next step, the composition-dependent activity of PtRuIr was mapped by means of cyclic voltammetry using a magnetron sputtered thin-film library. All measurements were performed in a scanning flow cell in acidic conditions (0.1 M HClO4) both in the absence and presence of isopropanol (0.1 M). Besides the assessment of activity, the effect of cycling in a wider potential window on the electrocatalytic behavior was also studied. To see if the observed trends can be translated to systems that are closer to real applications, compositions showing the highest activity were synthesized in the form of carbon-supported nanoparticles. Rotating disk electrode and scanning-flow cell measurements confirmed the behavior experienced in the case of the thin-film library. Looking at cyclic voltammograms, the beneficial role of Ir can be clearly identified: in addition to the observed low onset potential of isopropanol oxidation (0.05 VRHE) for the PtRu catalysts, Ir seems to help keeping the current between two oxidation peaks (Pt-Ru and Pt-Pt sides) constant. In order to see the benefit of Ir in real application, these catalysts are planned to be further tested in DIFC. Khanipour, P.; et. al., ACS Applied Materials & Interfaces 2020, 12 (30), 33670-33678.Mangoufis-Giasin, I.; et. al., Journal of Catalysis 2021, 400, 166-172.Kormanyos, A.; et. al., Journal of Catalysis 2021, 396.

Fabrication of an Ionomer-Free Electrode Containing Vertically Aligned One-Dimensional Nanostructures for Alkaline Membrane Fuel Cells

An ionomer-free electrode containing vertically aligned one-dimensional nanostructures was designed and fabricated for anion exchange membrane fuel cells (AEMFCs) by hydrothermal and vapor deposition processes. The silver-coated zinc oxide (ZnO) nanorod arrays (diameter = ca. 100 nm) were directly aligned with the gas diffusion layer (GDL), and these one-dimensional structures of the electrode enhanced the mass transport of the reactants to the catalytic surface via its short diffusion pathway and ionomer-free nature. Applied as a cathode, the membrane electrode assembly (MEA) containing the vertically aligned gas diffusion electrode showed about 80% increased maximum power density than that of MEA containing a conventional electrode, which consisted of randomly dispersed carbon-supported nanoparticle catalysts and an ionomer. Moreover, the durability test revealed that the prepared ionomer-free catalyst layer was a more stable electrode than the conventional one. Also, water consumption and oxygen transport characteristics of AEMFC with the ionomer-free electrode at the cathode were intensively investigated by varying the electrode thickness and compositions.

A channel flow cell with double disk electrodes for oxygen electroreduction study at elevated temperatures and pressures: Theory

• A new double-disk-electrode channel flow cell (DDECFC) was designed, constructed, and tested. • The DDECFC can be used for studying electrocatalysis such as ORR at elevated temperatures and pressures. • The hydrodynamic behaviors were numerically simulated, and experimentally characterized. • The hydrodynamic equation of the DDECFC was derived. • ORR on a carbon supported Pt catalyst was studied with the DDECFC. A new double-disk-electrode channel flow cell has been designed, constructed and tested. A theoretical treatment and implicit finite difference numerical simulations are presented, which permit the computation of the hydrodynamic behavior of this cell under steady state conditions, i.e., the diffusion limited current at the working electrode and the collection efficiency of the detector. The simulated results are consistent with those measured experimentally, indicating that our simulations appropriately describe the hydrodynamic behavior of this cell. The oxygen reduction reaction (ORR) on a carbon-supported nanoparticle Pt catalyst at both room temperature and 110 °C were preliminarily studied with this cell.

Effect of the Synthetic Method on the Properties of Ni-Based Hydrogen Oxidation Catalysts.

The latest progress in alkaline anion-exchange membranes has led to the expectation that less costly catalysts than those of the platinum-group metals may be used in anion-exchange membrane fuel cell devices. In this work, we compare structural properties and the catalytic activity for the hydrogen-oxidation reaction (HOR) for carbon-supported nanoparticles of Ni, Ni3Co, Ni3Cu, and Ni3Fe, synthesized by chemical and solvothermal reduction of metal precursors. The catalysts are well dispersed on the carbon support, with particle diameter in the order of 10 nm, and covered by a layer of oxides and hydroxides. The activity for the HOR was assessed by voltammetry in hydrogen-saturated aqueous solutions of 0.1 mol dm–1 KOH. A substantial activation by potential cycling of the pristine catalysts synthesized by solvothermal reduction is necessary before these become active for the HOR; in situ Raman spectroscopy shows that after activation the surface of the Ni/C, Ni3Fe, and Ni3Co catalysts is fully reduced at 0 V, whereas the surface of the Ni3Cu catalyst is not. The activation procedure had a smaller but negative impact on the catalysts synthesized by chemical reduction. After activation, the exchange-current densities normalized with respect to the ECSA (electrochemically active surface area) were approximately independent of composition but relatively high compared to catalysts of larger particle diameter.

Bimetallic Pd-Bi/C Catalysts Prepared by Grafting of Complexes with O-Donor Ligands

Bimetallic carbon-supported PdBi catalysts were prepared by grafting. To do so a soluble complex of bismuth with exchangeable O-donor ligands was selected, and the carbon support was functionalized to increase the number of surface functions. The grafting procedure was carried out by contacting the various supports with solutions of Pd and/or Bi complexes, to allow ligand exchange reactions to take place between the complexes and the surface O-groups. The grafted fragments were then activated into carbon-supported nanoparticles, which were characterized to unravel the impact of grafting experimental variables on the physico-chemical characteristics of the materials obtained. The PdBi/C catalysts were finally tested in the archetypal glucose selective oxidation reaction, to assess the impact of those characteristics on the catalytic performance. It was found that simultaneous grafting gave larger nanoparticles than consecutive grafting, while higher number of stable surface functions allowed to obtain small and nicely distributed bimetallic nanoparticles. However, the surface functions were found to be deleterious for the catalytic activity, and the placement of the Bi promoter with respect to Pd active phase was identified as another key parameter for the activity, with grafting allowing to compare neatly samples where Bi is underneath, above or beside Pd.

Realising the activity benefits of Pt preferential (111) surfaces for ethanol oxidation in a nanowire electrocatalyst

The commercialisation of direct ethanol fuel cells (DEFCs) is hindered by the low activity of the currently available electrocatalysts that are mainly carbon-supported nanoparticles (NPs). Here, we synthesised carbon-supported Pt nanowires (Pt/C NWs) by chemical reduction of metallic precursors at room temperature without using surfactants, templates, or stabilising agents. The synthesised Pt NWs were supported on high surface area carbon (Vulcan XC-72 R) with 40 wt%. Of metal loading concerning the support. The electroactivity of the synthesised NWs catalyst towards ethanol and CO (the dominant intermediate species) oxidation is investigated and tested in comparison with a commercial nanoparticle Pt/C electrocatalyst (named: Pt/C NPs). The electrooxidation of ethanol was investigated in acid media by CO-stripping, cyclic voltammetry, derivative voltammetry, chronoamperometry, steady-state polarisation curves, and in situ Fourier transform infrared spectroscopy (FTIR) experiments. The results showed that the synthesised Pt NWs are much more active than the Pt/C NPs catalyst, for both ethanol and CO-monolayer oxidation in acidic media. In situ FTIR data revealed that Pt NWs catalyst favours the formation of CO2 and acetic acid. This activity is mainly due to the existence of extended terraces, resulting in enhanced mobility of OHads and COads, facilitating the removal of COads from the catalyst surface and allowing better ethanol adsorption for further oxidation. Hence, 5-fold higher current density for ethanol oxidation is obtained. The NW morphology of Pt nanocatalysts results in very active materials towards ethanol oxidation and may provide a promising means of increasing the performance of anodes for DEFCs.

Recent Advances on Controlled Synthesis and Engineering of Hollow Alloyed Nanotubes for Electrocatalysis.

The past decade has witnessed great progress in the synthesis and electrocatalytic applications of 1D hollow alloy nanotubes with controllable compositions and fine structures. Hollow nanotubes have been explored as promising electrocatalysts in the fuel cell reactions due to their well-controlled surface structure, size, porosity, and compositions. In addition, owing to the self-supporting ability of 1D structure, hollow nanotubes are capable of avoiding catalyst aggregation and carbon corrosion during the catalytic process, which are two other issues for the widely investigated carbon-supported nanoparticle catalysts. It is currently a great challenge to achieve high activity and stability at a relatively low cost to realize commercialization of these catalysts. An overview of the structural and compositional properties of 1D hollow alloy nanotubes, which provide a large number of accessible active sites, void spaces for electrolytes/reactants impregnation, and structural stability for suppressing aggregation, is presented. The latest advances on several strategies such as hard template and self-templating methods for controllable synthesis of hollow alloyed nanotubes with controllable structures and compositions are then summarized. Benefiting from the advantages of the unique properties and facile synthesis approaches, the capability of 1D hollow nanotubes is then highlighted by discussing examples of their applications in fuel-cell-related electrocatalysis. Finally, the remaining challenges and potential solutions in the field are summarized to provide some useful clues for the future development of 1D hollow alloy nanotube materials.

Synthesis and growth mechanism of carbon-supported nanoparticle catalysts by physical vapor deposition onto a liquid medium substrate

Metal nanoparticles (NPs) have been extensively investigated owing to their unique properties attributing to their high surface/bulk ratio and finite number of atoms. However, the thermodynamic instability of NPs, which originates from their finite size, limits their practical applications. Hence, carbon-supported Pt NPs are synthesized onto carbon-containing liquid substrates via direct one-step sputtering. In order to successfully produce uniform Pt NPs via sputtering using various ionic liquids as non-volatile liquid substrates, special conditions are required, and the relationship between ionic liquids and particle surfaces should be investigated. It has been reported that anions and carbon supports of ionic liquids significantly affect the dispersion and synthesis of Pt NPs. In this study, we proposed a mechanism underlying the chemical bonding between anions and carbon supports and verified it using X-ray photoelectron spectroscopy and infrared spectroscopy.

Synergistic Effect on the Activity of Fe+ZrO2 Non-PGM ORR Catalysts for PEMFC

High cost and limited availability of platinum-based catalysts for the Oxygen Reduction Reaction (ORR) is a major hurdle towards the commercialization of Proton Exchange Membrane Fuel Cell (PEMFC) systems. Until today, replacing Pt by Pt-free and finally by noble-metal-free ORR catalysts is still restricted to the laboratory scale. High activity and durability are the main requirements for new catalysts. The currently most favored materials are based on the MNxCy system (M = Fe, Co) due to their low cost and reasonable ORR activity, but they still cannot be commercialized due to their poor stability in corrosive environment [1, 2]. On the other hand, valve-metal oxides as non-PGM ORR catalysts are promising based on their stability in acid, but their ORR activity still needs to be improved [3, 4]. Recently, our group published an article in which the synthesis of carbon-supported zirconia (ZrO2) nanoparticles has been optimized towards ORR activity by varying the heat treatment atmosphere and temperature [5]. Based on our findings, we concluded that the intrinsic ORR activity of the pure valve-metal oxides is far too low to be practically employed in fuel cells. Since it is hypothesized that the active sites correlate with the presence of oxygen vacancies or uncoordinated metal sites at the oxide surface [6, 7], a way to enhance their ORR activity would be to substitute part of the valve metals in the oxide with aliovalent metals. In this study, we have chosen iron as a substituent, since it is ORR-active and since it is known that it can be incorporated into the ZrO2 structure [8]. In this contribution, a series of ORR catalysts consisting of Fe containing ZrO2 nanoparticles and supported on graphitized Ketjen-Black carbon (ZrO2/KBGraph) are studied. In order to get a homogeneous mixture of the two metals at the molecular level, the synthesis route employed two soluble organometallic precursors, viz., zirconium (IV) tetra-tert-butyl dichloro phthalocyanine (ZrCl2Pc(tBu)4) and iron(II) tetra-tert-butyl phthalocyanine (FePc(tBu)4). The carbon support was first impregnated with the mixed precursor solution and then heat-treated as described in [9]. From XRD characterization it is evident that we obtain ZrO2 particles with a particle size much smaller than 10 nm. Electrochemical measurements of the ORR activity are performed at 20 °C using a thin-film rotating disk electrode (RDE) setup in 0.1 M HClO4 at 20 °C, 1600 rpm, reporting the capacitively-corrected anodic scans [10]. As shown in Figure 1, the carbon-supported nanoparticles prepared by adding Fe to ZrO2 show a significantly increased activity when compared to pure Fe or ZrO2 samples heat treated under the same conditions. It is thus evident that a clear synergistic effect between the two components results in a much more ORR-active catalyst. A detailed structural characterization of the active catalyst and their further optimization will be the focus of this presentation.

Synthesis optimization of carbon-supported ZrO2 nanoparticles from different organometallic precursors

We report here the synthesis of carbon-supported ZrO2 nanoparticles from zirconium oxyphthalocyanine (ZrOPc) and acetylacetonate [Zr(acac)4]. Using thermogravimetric analysis (TGA) coupled with mass spectrometry (MS), we could investigate the thermal decomposition behavior of the chosen precursors. According to those results, we chose the heat treatment temperatures (THT) using partial oxidizing (PO) and reducing (RED) atmosphere. By X-ray diffraction we detected structure and size of the nanoparticles; the size was further confirmed by transmission electron microscopy. ZrO2 formation happens at lower temperature with Zr(acac)4 than with ZrOPc, due to the lower thermal stability and a higher oxygen amount in Zr(acac)4. Using ZrOPc at THT ≥900 °C, PO conditions facilitate the crystallite growth and formation of distinct tetragonal ZrO2, while with Zr(acac)4 a distinct tetragonal ZrO2 phase is observed already at THT ≥750 °C in both RED and PO conditions. Tuning of ZrO2 nanocrystallite size from 5 to 9 nm by varying the precursor loading is also demonstrated. The chemical state of zirconium was analyzed by X-ray photoelectron spectroscopy, which confirms ZrO2 formation from different synthesis routes.

Pd-M/C (M = Pd, Cu, Pt) Electrocatalysts for Oxygen Reduction Reaction in Alkaline Medium: Correlating the Electronic Structure with Activity.

The increasing global needs for clean and renewable energy have fostered the design of new and highly efficient materials for fuel cells applications. In this work, Pd-M (M = Pd, Cu, Pt) and Pt nanoparticles were prepared by a green synthesis method. The carbon-supported nanoparticles were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. A comprehensive electronic and structural characterization of these materials was achieved using X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Their electrochemical properties were investigated by cyclic voltammetry, while their activities for the ORR were characterized using steady-state polarization experiments. The results revealed that the bimetallic nanoparticles consist of highly crystalline nanoalloys with size around 5 nm, in which the charge transfer involving Pd and M atoms affects the activity of the electrocatalysts. Additionally, the samples with higher ORR activity are those whose d-band center is closer to the Fermi level.

Functionalized Natural Carbon-Supported Nanoparticles as Excellent Catalysts for Hydrocarbon Production.

We report a one-pot and eco-friendly synthesis of carbon-supported cobalt nanoparticles, achieved by carbonization of waste biomass (rice bran) with a cobalt source. The functionalized biomass provides carbon microspheres as excellent catalyst support, forming a unique interface between hydrophobic and hydrophilic groups. The latter, involving hydroxyl and amino groups, can catch much more active cobalt nanoparticles on surface for Fischer-Tropsch synthesis than chemical carbon. The loading amount of cobalt on the final catalyst is much higher than that prepared with a chemical carbon source, such as glucose. The proposed concept of using a functionalized natural carbon source shows great potential compared with conventional carbon sources, and will be meaningful for other fields concerning carbon support, such as heterogeneous catalysis or electrochemical fields.