Fuel Cell Reactions Research Articles

Ultrafine two-dimensional alloyed PdCu nanosheets-constructed three-dimensional nanoflowers enable efficient ethylene glycol electrooxidation

Constructing efficient catalysts for the electrooxidation of fuels is of vital importance for realizing the commercialization of fuel cells. Unfortunately, most of catalysts (e.g. Pt) suffer from limited activity and poor durability for the electrooxidation of liquid fuel. Also, the drawbacks of extremely high cost and nature scarcity have also severely hindered their large-scale applications. Here, we demonstrated the synthesis of a new class of well-defined and three-dimensional (3D) flower-like nanocatalysts which assembled by ultrafine two-dimensional (2D) alloyed PdCu nanosheets. Structurally, the as-obtained PdCu alloy nanoflowers (NFs) possessed high surface area with abundant surface active sites. Benefiting from the unique structural properties and the strong alloy effect, the as-obtained PdCu NFs can display greatly enhanced performances toward ethylene glycol oxidation reaction (EGOR) with the mass/specific activity of 4714.1 mA mg−1/13.7 mA cm−2, which are 4.4 and 6.85 times of Pd/C catalysts, respectively. Most strikingly, such 2D nanosheets-constructed 3D nanoflower-like structure also enables the PdCu catalysts with high long-term stability for EGOR. As a proof of concept, this work not only presents the rational design and construction of catalysts with well-defined structure for the fuel cells reactions but also provides a promising method to largely promote the electrochemical performances of catalysts.

Cu@Pt catalysts prepared by galvanic replacement of polyhedral copper nanoparticles for polymer electrolyte membrane fuel cells

Polyhedral copper nanoparticles are prepared by a hydrothermal method, followed by galvanic replacement with platinum precursor in ethylene glycol to prepare bimetallic Cu@Pt electrocatalysts. The as-prepared bimetallic Cu@Pt catalyst are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and inductive coupled plasma atomic emission spectrometer. The electrochemical properties of the resulted Cu@Pt electrocatalysts with different compositions are investigated for methanol oxidation reaction and oxygen reduction reaction. The bimetallic Cu@Pt electrocatalysts with low platinum loading demonstrate high Pt utilization efficiency in fuel cell reactions. The methanol oxidation reaction mass activity for Cu@Pt-8 catalyst is 791 A g−1, 5.1 times higher than that of the commercial Pt/C. The highest oxygen reduction reaction mass activity is found for Cu@Pt-25 (93 A g−1 at 0.9 V versus relative hydrogen electrode), which represents 61% enhancement relative to that of a commercial Pt/C (54 A g−1). It is believed that the superior performance of the as-prepared bimetallic Cu@Pt catalyst is mostly attributed to the improved Pt utilization and facilitated mass transport originating from the porous structure.

Core@Shelled Co/CoO Embedded Nitrogen-Doped Carbon Nanosheets Coupled Graphene as Efficient Cathode Catalysts for Enhanced Oxygen Reduction Reaction in Microbial Fuel Cells

High-efficiency oxygen reduction reaction (ORR) catalysts are crucial for facilitating the large-scale exploitation of electrochemical energy storage and conversion technologies. Herein, we demonstrate a carbon-based metal hybrid, which offers a higher electrocatalytic activity than that of the individual composite by optimizing the electronic modulation effect from suitable microstructure. The resulting cobalt@cobalt oxide nanoparticles embedded in N-doped carbon shell couple with hierarchical porous graphene (GCN–Co@CoO), exhibiting a significantly enhanced ORR activity in alkaline solution and highlighting a synergistic effect between N-doped carbon shell and metallic Co species. More precisely, the GCN–Co@CoO hybrid pyrolyzed at 800 °C achieves a more positive half-wave potential of −0.194 V (vs SCE) and superior limiting current of 4.91 mA cm–2. Moreover, the GCN–Co@CoO composite also shows an outstanding tolerance to methanol crossover effects and long-term stability. Furthermore, based on the GCN–Co@CoO cathode catalyst, the self-assembled microbial fuel cells perform a maximum power density of 611 ± 9 mW m–2 at a high current density of 1869 ± 24 mA m–2.

Platinum Group Nanowires for Efficient Electrocatalysis

AbstractAt the frontier of electrocatalysis, there is a research endeavor focusing on platinum group (PG)‐based nanomaterials due to their fantastic morphological diversity and superior catalytic performance. In contrast to catalysts with other morphologies, nanowire catalysts show great potential in electrocatalysis due to their large surface area, abundant high‐index facet sites for catalysis, quick electron and mass transport for better conductivity, promotion for recycling and 3D structure construction, and good prohibition for vulnerability to dissolution, Ostwald ripening, and aggregation. Yet, it is challenging to endow PG nanowires with a precise control on size, shape, and composition. Here, the recently available strategies for designing PG‐based nanowire electrocatalysts with enhanced activity and stability are highlighted. A summary of the synthetic methods for generating different kinds of nanowires with detailed experimental parameters is also provided, with particular emphases on the recent progress of PG‐based nanowires for boosting the electrocatalytic reactions, including fuel cell reactions, hydrogen evolution reaction, and oxygen evolution reaction. In the final section, available perspectives on the future development of PG‐based nanowires for enhanced catalytic performances are discussed separately.

PdNi alloy nanoparticles assembled on cobalt ferrite-carbon black composite as a fuel cell catalyst

PdNi alloy nanoparticles (NPs) were synthesized and then readily assembled on the composite of cobalt ferrite NPs with Vulcan XC-72 carbon (CoFe2O4-VC). The electrocatalyst performance of the yielded PdNi/CoFe2O4-VC composite was tested in borohydride fuel cell reactions in alkaline media. The structure/morphology of colloidal CoFe2O4 and PdNi alloy NPs along with the yielded CoFe2O4-VC composite and PdNi/CoFe2O4-VC electrocatalyst were examined by TEM, powder XRD and ICP-MS. Both monodisperse CoFe2O4 and PdNi alloy NPs with 11 and 4 nm average size, respectively, were discernible over the VC support material by the TEM images of the electrocatalyst. The loading ratio of CoFe2O4 and PdNi alloy NPs in the composite was found to be 16.1 wt% and 2.7 wt%, respectively, as determined by ICP-MS. The performance of PdNi/CoFe2O4-VC as a novel electrocatalyst for oxygen reduction (ORR) and borohydride oxidation (BOR) reactions in alkaline media was studied by voltammetric techniques using a rotating disk electrode. ORR and BOR parameters such as number of exchanged electrons and kinetic current density were calculated. The results revealed that PdNi/CoFe2O4-VC electrocatalyst was highly efficient for both ORR and BOR with exchange of 3.2 and 6.6 electrons, respectively.

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.

The Comparability of Pt to Pt‐Ru in Catalyzing the Hydrogen Oxidation Reaction for Alkaline Polymer Electrolyte Fuel Cells Operated at 80 °C

AbstractThe Pt‐catalyzed hydrogen oxidation reaction (HOR) for alkaline polymer electrolyte fuel cells (APEFCs) has been one of the focus subjects in current fuel‐cell research. The Pt catalyst is inferior for HOR in alkaline solutions, and alloying with Ru is an effective promotion strategy. APEFCs with Pt‐Ru anodes have provided a performance benchmark over 1 W cm−2 at 60 °C. The Pt anode is now found to be in fact as good as the Pt‐Ru anode for APEFCs operated at elevated conditions. At 80 °C with appropriate gas back‐pressure, the cell with a Pt anode exhibits a peak power density of about 1.9 W cm−2, which is very close to that with a Pt‐Ru anode. Even by decreasing the anode Pt loading to 0.1 mg cm−2, over 1.5 W cm−2 can still be achieved at 80 °C. This finding alters the previous understanding about the Pt catalyzed HOR in alkaline media and casts a new light on the development of practical and high‐power APFEC technology.

The Comparability of Pt to Pt-Ru in Catalyzing the Hydrogen Oxidation Reaction for Alkaline Polymer Electrolyte Fuel Cells Operated at 80 °C.

The Pt-catalyzed hydrogen oxidation reaction (HOR) for alkaline polymer electrolyte fuel cells (APEFCs) has been one of the focus subjects in current fuel-cell research. The Pt catalyst is inferior for HOR in alkaline solutions, and alloying with Ru is an effective promotion strategy. APEFCs with Pt-Ru anodes have provided a performance benchmark over 1 W cm-2 at 60 °C. The Pt anode is now found to be in fact as good as the Pt-Ru anode for APEFCs operated at elevated conditions. At 80 °C with appropriate gas back-pressure, the cell with a Pt anode exhibits a peak power density of about 1.9 W cm-2 , which is very close to that with a Pt-Ru anode. Even by decreasing the anode Pt loading to 0.1 mg cm-2 , over 1.5 W cm-2 can still be achieved at 80 °C. This finding alters the previous understanding about the Pt catalyzed HOR in alkaline media and casts a new light on the development of practical and high-power APFEC technology.

Plasmon-Induced Electrocatalysis with Multi-Component Nanostructures.

Noble metal nanostructures are exceptional light absorbing systems, in which electron–hole pairs can be formed and used as “hot” charge carriers for catalytic applications. The main goal of the emerging field of plasmon-induced catalysis is to design a novel way of finely tuning the activity and selectivity of heterogeneous catalysts. The designed strategies for the preparation of plasmonic nanomaterials for catalytic systems are highly crucial to achieve improvement in the performance of targeted catalytic reactions and processes. While there is a growing number of composite materials for photochemical processes-mediated by hot charge carriers, the reports on plasmon-enhanced electrochemical catalysis and their investigated reactions are still scarce. This review provides a brief overview of the current understanding of the charge flow within plasmon-enhanced electrochemically active nanostructures and their synthetic methods. It is intended to shed light on the recent progress achieved in the synthesis of multi-component nanostructures, in particular for the plasmon-mediated electrocatalysis of major fuel-forming and fuel cell reactions.

Binary CuPt alloy nanoparticles assembled on reduced graphene oxide-carbon black hybrid as efficient and cost-effective electrocatalyst for PEMFC

Addressed herein is the synthesis of binary CuPt alloy nanoparticles (NPs), their assembly on reduced graphene oxide (rGO), Vulcan XC72 (VC) and their hybrid (rGO-VC) to be utilized as electrocatalysts for fuel cell reactions (HOR and ORR) in acidic medium and PEMFC tests. The synthesis of nearly-monodisperse Cu45Pt55 alloy NPs was achieved by using a chemical reduction route comprising the reduction of commercially available metal precursors in a hot surfactant solution. As-synthesized Cu45Pt55 alloy NPs were then assembled on three support materials, namely rGO, VC and rGO-VC) via liquid phase self-assembly method. After the characterization, the electrocatalysts were prepared by mixing the yielded materials with Nafion and their electrocatalysis performance was investigated by studying CV and LSV for HOR and ORR in acidic medium. Among the three electrocatalysts tested, Cu45Pt55/rGO-VC hybrid showed the highest catalytic activity with ECSA of 119 m2 g−1 and mass activity of 165 mA mg−1Pt. After the evaluation of electrochemical performance of the three prepared electrocatalysts, their performance was then evaluated in fuel cell conditions. In similar to electrochemical activities, the Cu45Pt55/rGO-VC hybrid electrocatalyst showed a superior fuel cell performance and power output by providing a maximum power of 480 mW cm−2 with a relatively low Pt loading (0.28 mg cm−2). Additionally, the Cu45Pt55/rGO-VC hybrid electrocatalyst exhibited substantially better activity as compared to Pt/rGO-VC electrocatalyst. Therefore, the present study confirmed that alloying Pt with Cu enhances the catalytic activity of Pt metal along with the help of beneficial features of rGO-VC hybrid support material. It should be noted that this is the first example of studying PEMFC performance of CuPt alloy NPs supported on rGO, VC and rGO-VC hybrid.

Revealing the Role of Phase Structures of Bimetallic Nanocatalysts in the Oxygen Reduction Reaction

The ability to tune the atomic-level structure of alloy nanoparticles (NPs) is essential for the design and preparation of active and stable catalysts for fuel cell reactions such as the oxygen red...

An Efficient Electrocatalyst based on Platinum Incorporated into N,S co-doped Porous Graphene for Oxygen Reduction Reaction in Microbial Fuel Cell

An Efficient Electrocatalyst based on Platinum Incorporated into N,S co-doped Porous Graphene for Oxygen Reduction Reaction in Microbial Fuel Cell

Construction of Pt/graphitic C3N4/MoS2 heterostructures on photo-enhanced electrocatalytic oxidation of small organic molecules

Low temperature fuel cells, with the features of clean, environmental friendliness, and high energy density, are considered as ideal future green energy sources. It has been recently demonstrated that the activities and stabilities of traditional fuel cell reactions can be improved by using photo-functional electrodes with assistance of light illumination. Two-dimensional (2D) heterostructure of g-C3N4/MoS2 was demonstrated to be a promising photocatalyst. Herein, we used g-C3N4/MoS2 nanosheets as a photo-functional substrate for the decoration of Pt nanoparticles and then applied on fuel cell electrocatalytic reactions. Comparing with traditional electrocatalytic reactions, the electrocatalytic performances of the as-synthesized Pt/g-C3N4/MoS2 for the oxidation of methanol, ethanol, and formic acid upon visible light illumination are improved with 6.5, 2.2, and 2.5 times, respectively. The decisive factors in the improved catalytic performances are the synergistic effect of photo&electro-process and the effective charge separation in the designed 2D/2D g-C3N4/MoS2 heterostructure.

Analysis of Proton Exchange Membrane Fuel Cell reactant gas dynamic response and distribution quality

The lifetime of automotive fuel cells is one of the key issues that restrict their commercialization. Previous research results have shown that frequent changing load conditions are the main reason leading to its life attenuation. At present, the dynamic response characteristics and mechanism of fuel cells are not yet clear. The control and structural design for the key components of the long-life, high-dynamic response fuel cell systems requires theoretical guidance. To solve this problem, this paper studies the dynamic response characteristics and distribution quality of reactant gas in the process of load change. In this paper, a three-dimension, five serpentine channels, single-phase model of proton exchange membrane fuel cell (PEMFC) single cell is built. A new method is created to describe the variation of fuel cell voltage and distribution of reactant gases under the condition of steady state and dynamic state. The effects of working pressure, stoichiometric ratio and variable loading amplitude on the performance of the fuel cell were analyzed in detail, and the gas distribution on the electrode surface under various operating conditions was quantitatively studied. The final conclusions have important guiding significance for the selection of fuel cell operation parameters and variable loading parameters and optimization of operating conditions. The research methods and conclusions of this paper will provide a reference for optimal control and structural design of high-dynamic-response fuel cells, providing a theoretical basis for long-life research of fuel cells.

Effect of Chemical Composition on the Nanoscale Ordering Transformations of Physical Mixtures of Pd and Cu Nanoparticles

The nanoscale composition and structure of alloy catalysts affect their performance in heterogeneous catalysis. In particular, previous reports indicated that PdCu nanoparticles are more efficient as catalysts in fuel cell reactions than monometallic Pd catalysts. To understand the structural transformations of PdCu nanoalloys, real-time in situ synchrotron X-ray diffraction was used to examine the temperature-induced evolution of physical mixtures of Pd and Cu nanoparticles. Ex situ transmission electron microscopy measurements provide additional information about the size, phase, composition, and ordering of the nanoparticle mixtures. The results for PdCu mixtures of composition 1 : 1 and 3 : 1 supported on SiO2 are presented in detail here. The annealing procedure involved two stages: (a) isothermal annealing at 450°C and (b) ramped annealing from 450°C to 750°C, both in forming gas atmospheres. We found the ordered B2 phase to be formed at 450°C in all compositions studied. Ramped annealing of PdCu 1 : 1 mixtures from 450°C to 750°C leads to the transformation of the B2 phase into two different alloys, one rich in Cu and the other rich in Pd. This structural evolution bears the signature of spinodal decomposition and is different from that of PdCu bulk alloys. In PdCu 3 : 1 mixtures, the B2 phase dominates after isothermal annealing at 450°C, but a significant disordered alloy fcc phase is also formed. During annealing at 750°C, the disordered fcc phase grows at the expense of the B2 phase. These findings are important for the understanding of thermal activation of PdCu nanocatalysts for fuel cells.

Cover Feature: Rational Design of Superior, Coking‐Resistant, Nickel‐Based Anodes through Tailoring Interfacial Reactions for Solid Oxide Fuel Cells Operated on Methane Fuel (ChemSusChem 18/2018)

Cover Feature: Rational Design of Superior, Coking‐Resistant, Nickel‐Based Anodes through Tailoring Interfacial Reactions for Solid Oxide Fuel Cells Operated on Methane Fuel (ChemSusChem 18/2018)

Simultaneous boron (B) removal and electricity generation from domestic wastewater using duckweed-based wastewater treatment reactors coupled with microbial fuel cell

Boron removal from water environment is a critical issue for scientific spotlight because its removal from wastewater is difficult and costly with conventional treatment method. Herein, an innovative, cost effective and attractive method which depends on duckweed-based wastewater treatment systems coupled with microbial fuel cell reactor (DWWT-MFC) was investigated for B-polluted domestic wastewater treatment and simultaneous electricity generation for the first time in an eco-technological study. Lemna gibba L. was selected as a model duckweed species, and different reactors were also designed to identify which mechanisms are dominant for B removal in a DWWT-MFC reactor matrix. DWWT-MFC reactor achieved 71% B removal in experiment period, and the plant effect on B removal mechanisms in the reactor matrix was recorded as 37.7 ± 4.92% (F = 2.543, p < 0.05). However, supplementary aeration and microbial effects on B removal were determined as negligible. Average maximum voltage output was found as 1.47 V, and maximum power density was 34.8 mW/m2 at a current density of 43.9 mA/m2 with supplementary aeration. Moreover, DWWT-MFC reactor achieved 84%, 81% and 76% of COD, NH4+ and PO43− removal efficiencies, respectively. Moreover, L. gibba grew well in the anode chamber of DWWT-MFC with an average biomass yield of 218 ± 43 g/m2 and a total chlorophyll (a+b) concentration of 30.2 mg g−1, which indicates that anolyte environment was not toxic for L. gibba growth. Consequently, it can be suggested that environmental experts may use DWWT-MFC as an efficient removal method to treat B from domestic wastewater and to produce bioelectricity.

Nano-engineered hexagonal PtCuCo nanocrystals with enhanced catalytic activity for ethylene glycol and glycerol electrooxidation

Abstract Although great advances have been achieved in the field of fuel cells, the lack of cost-efficient electrocatalysts is still the grand challenge impeding the practical application of fuel cells. To this end, rational design of efficient multicomponent electrocatalysts with both high activity and stability is highly momentous for fuel cell reaction. Herein, a facile approach to controllably engineer trimetallic hexagonal PtCuCo nanocrystals (NCs) as highly active and durable liquid fuel electrooxidation catalysts is reported. Impressively, after the incorporation of Cu and Co into Pt, the electronic structures of Pt remarkably modified, leading to the enhancement of electrocatalytic performances. The optimized hexagonal PtCuCo NCs were demonstrated to display outstanding activities of 4926.4 and 3519.9 mA mg−1 for the electrooxidation of ethylene glycol (EG) and glycerol, in comparison with Pt/C catalysts. The greatly improved activity of hexagonal PtCuCo NCs is ascribed to the highly exposed surface active areas and the electronic effects among Pt, Cu, and Co. More importantly, the trimetallic hexagonal nanocatalysts also display great durability with little variations in composition, structure, and activity, showing an advanced class of nanocatalysts for fuel cells and beyond.

Rational Design of Superior, Coking-Resistant, Nickel-Based Anodes through Tailoring Interfacial Reactions for Solid Oxide Fuel Cells Operated on Methane Fuel.

The reaction between a Ni-Y2 O3 -stabilized ZrO2 (Ni-YSZ) cermet anode and La5.4 WO12-δ (LW) during cell fabrication is utilized to reduce carbon deposition in solid oxide fuel cells operated on methane fuel. The effect of the phase reactions on the microstructure, electrical conductivity, chemical interactions, and coking resistance of the anodes are systematically investigated. Nix Wy and La-doped YSZ are formed by phase reactions and the synergistic effect between them increases the coking resistance dramatically. 2 wt % is demonstrated to be the optimal amount of LW to modify Ni-YSZ to achieve best coking resistance. The cell with Ni-YSZ-2 wt % LW anode demonstrates a superior peak power density of 943 mW cm-2 at 800 °C with humidified methane as fuel, which is 10 % higher than that of Ni-YSZ (859 mW cm-2 ). Furthermore, the cell is stable for 200 h in methane fuel with no clear performance degradation while the cell with unmodified anode fails after 0.5 h's operation. In summary, we provide a new way to rationally design Ni-based cermet anode with high electrocatalytic activity and excellent coking resistance.

Partially Oxidized Bimetallic Nanocrystals as Efficient Non‐Noble Metal Alcohol Electrooxidation Catalysts

AbstractAlthough extensive efforts have been devoted to pursuing active nanomaterials for fuel cell reactions, they still suffer from serious structure changes and loss of active sites during the electrocatalysis. Herein, we have successfully constructed bimetallic Cu−Ni nanocrystals with unique yolk‐shell architecture via partial oxidation, which can largely release the particle expansion and effectively prevent the particle from aggregation and dissolution during the electrocatalysis. As a consequent, the optimized Cu−Ni yolk‐shell electrocatalyst delivers excellent durability with only 19.6 % activity decay after 10 h‐methanol oxidation reaction (MOR), in contrast with that of the commercial Pt/C (96.0 %), and can even maintain 62.6 % activity after long‐term MOR (5 days). XPS analysis indicates that the large downshift of d‐band center of Cu−Ni yolk‐shell electrocatalyst leads to the release of “poison effect” for enhancing the alcohol electrooxidation. The present work provides a new approach for achieving low‐cost catalysts with ultrahigh stability for electrooxidation and beyond.