Hamish A. Miller

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis

The energetic convenience of electrolytic water splitting is limited by thermodynamics. Consequently, significant levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kWh kg(-1)H2. Electrochemical reforming allows the overcoming of such thermodynamic limitations by replacing oxygen evolution with the oxidation of biomass-derived alcohols. Here we show that the use of an original anode material consisting of palladium nanoparticles deposited on to a three-dimensional architecture of titania nanotubes allows electrical energy savings up to 26.5 kWh kg(-1)H2 as compared with proton electrolyte membrane water electrolysis. A net energy analysis shows that for bio-ethanol with energy return of the invested energy larger than 5.1 (for example, cellulose), the electrochemical reforming energy balance is advantageous over proton electrolyte membrane water electrolysis.

Electrooxidation of Ethylene Glycol and Glycerol on Pd-(Ni-Zn)/C Anodes in Direct Alcohol Fuel Cells

The electrooxidation of ethylene glycol (EG) and glycerol (G) has been studied: in alkaline media, in passive as well as active direct ethylene glycol fuel cells (DEGFCs), and in direct glycerol fuel cells (DGFCs) containing Pd-(Ni-Zn)/C as an anode electrocatalyst, that is, Pd nanoparticles supported on a Ni-Zn phase. For comparison, an anode electrocatalyst containing Pd nanoparticles (Pd/C) has been also investigated. The oxidation of EG and G has primarily been investigated in half cells. The results obtained have highlighted the excellent electrocatalytic activity of Pd-(Ni-Zn)/C in terms of peak current density, which is as high as 3300 A g(Pd)(-1) for EG and 2150 A g(Pd)(-1) for G. Membrane-electrode assemblies (MEA) have been fabricated using Pd-(Ni-Zn)/C anodes, proprietary Fe-Co/C cathodes, and Tokuyama A-201 anion-exchange membranes. The MEA performance has been evaluated in either passive or active cells fed with aqueous solutions of 5 wt % EG and 5 wt % G. In view of the peak-power densities obtained in the temperature range from 20 to 80 °C, at Pd loadings as low as 1 mg cm(-2) at the anode, these results show that Pd-(Ni-Zn)/C can be classified amongst the best performing electrocatalysts ever reported for EG and G oxidation.

A Pd/C-CeO2 Anode Catalyst for High-Performance Platinum-Free Anion Exchange Membrane Fuel Cells

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM-FCs). The anion exchange membrane fuel cell (AEM-FC) has long been proposed as a solution as non-Pt metals may be employed. Despite this, few examples of Pt-free AEM-FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt-free AEM-FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt-free AEM-FC that employs a mixed carbon-CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM-FC tests run on dry H2 and pure air show peak power densities of more than 500 mW cm(-2) .

Electro-oxidation of ethylene glycol and glycerol at palladium-decorated FeCo@Fe core-shell nanocatalysts for alkaline direct alcohol fuel cells : functionalized MWCNT supports and impact on product selectivity

Half-cell reactions and alkaline direct ethylene glycol and glycerol fuel cells (DEGFC and DGFC) have been studied on Pd-based ternary core–shell (FeCo@Fe@Pd) nanocatalyst using multi-walled carbon nanotubes bearing carboxylic (MWCNT-COOH) and sulfonic acid (MWCNT-SO3H) as supporting platforms. The core–shell–shell nature of this nanocatalyst, obtained via the “microwave-induced top-down nanostructuring and decoration”, was clearly proven from atomic resolution transmission electron microscopy (ARTEM). The functional groups of the MWCNTs show a huge impact on the physico-chemical properties of the FeCo@Fe@Pd nanocatalyst towards the electrocatalytic oxidation of EG and GLY in alkaline media. The FeCo@Fe@Pd on –COOH-treated MWCNTs showed the small particle size of ca. 7.4 nm, uniform loading of the catalyst on the support, large electrochemically-active surface area and enhanced electrocatalytic activity compared to the FeCo@Fe@Pd on –SO3H-bearing MWCNTs. As a preliminary test, FeCo@Fe@Pd/MWCNT-COOH was used for passive, air-breathing anion-exchange membrane based fuel cells (AEM-DEGFC and AEM-DGFC). The analysis of the exhaust products, established using NMR spectroscopy, revealed a high selectivity towards the complete oxidation of both EG and GLY under benign experimental conditions.

Direct Alcohol Fuel Cells: Toward the Power Densities of Hydrogen‐Fed Proton Exchange Membrane Fuel Cells

A 2 μm thick layer of TiO2 nanotube arrays was prepared on the surface of the Ti fibers of a nonwoven web electrode. After it was doped with Pd nanoparticles (1.5 mgPd  cm(-2) ), this anode was employed in a direct alcohol fuel cell. Peak power densities of 210, 170, and 160 mW cm(-2) at 80 °C were produced if the cell was fed with 10 wt % aqueous solutions of ethanol, ethylene glycol, and glycerol, respectively, in 2 M aqueous KOH. The Pd loading of the anode was increased to 6 mg cm(-2) by combining four single electrodes to produce a maximum peak power density with ethanol at 80 °C of 335 mW cm(-2) . Such high power densities result from a combination of the open 3 D structure of the anode electrode and the high electrochemically active surface area of the Pd catalyst, which promote very fast kinetics for alcohol electro-oxidation. The peak power and current densities obtained with ethanol at 80 °C approach the output of H2 -fed proton exchange membrane fuel cells.

Energy Efficiency of Alkaline Direct Ethanol Fuel Cells Employing Nanostructured Palladium Electrocatalysts

Carbon supported nanostructured palladium or palladium alloys are considered the best performing anode electrocatalysts currently employed in alkaline electrolyte membrane direct ethanol fuel cells (AEM‐DEFCs). High initial peak power densities are generally obtained as Pd preferentially favors the selective oxidation of ethanol forming acetate thus avoiding strongly poisoning intermediates such as CO. However, few studies exist that investigate DEFC performance in terms of both energy efficiency and discharge energy density, as well as power density depending on the concentration of fuel. In this paper we have determined such parameters for room temperature air breathing AEM‐DEFCs equipped with Pd based anodes, anion exchange membranes and FeCo/C cathode electrocatalysts. Combined with the optimization of the fuel composition a maximum energy efficiency of ≈7 % was obtained for this AEM‐DEFC. Such a performance suggests that devices of this type are suitable for supplying low power applications such as small portable electronic devices.

Nanotechnology in electrocatalysis for energy

PART 1: FUNDAMENTALS Chapter 1: Introduction 1.1 Key concepts 1.2 Energy and Resources 1.3 Environmental concerns 1.4 Renewable energy resources 1.4.1 The EROEI and the Life Cycle Analysis 1.4.2 The role of hydrogen and energy vectors 1.5 Fuel Cells as Power Sources 1.6 Electrolytic Hydrogen Production 1.7 CO2 Electroreduction 1.8 Electrocatalysis and the need for nanotechnology 1.9 This books approach References Chapter 2: A birds eye view of energy related electrochemistry 2.1 Key concepts 2.2 Thermodynamics 2.2.1 The Electrochemical Cell 2.2.2 Electrochemical reaction and the Nernst equation 2.3 Electrochemical kinetics 2.3.1 Charge Transfer 2.3.2 Mass transfer 2.3.3 Adsorption 2.4 Electrochemical Techniques 2.4.1 Voltammetry 2.4.2 Rotating Disk and Rotating Ring Disk methods 2.5 Major Energy Related Electrochemical Reactions 2.5.1 Hydrogen oxidation and evolution reactions 2.5.2 Oxygen evolution and oxidation reaction 2.5.3 Methanol Oxidation 2.5.4 Ethanol electroxidation 2.5.5 Other Alcohols 2.5.6 Formic acid 2.5.7 CO2 electroreduction reaction References Chapter 3: Electrochemical device for energy conversion and storage 3.1 Key concepts 3.2 Fuel Cells - General Background 3.2.1 Components of PEM fuel cell 3.2.2 Fuel cell key performance parameters 3.2.3 Main operational parameters 3.3 Major low temperature fuel cells 3.3.1 Hydrogen PEMFC 3.3.2 Direct Methanol Fuel Cells 3.3.3 Direct Alcohol Fuel Cells 3.4 Electrolysis - General Background 3.4.1 Alkaline Electrolysis 3.4.2 Zero Gap Electrolysis 3.4.3 The proton exchange membrane water electrolyzer 3.4.4 Electrolysis with anode reactions other than OER References Chapter 4: Factors affecting design 4.1 Key concepts 4.2 Technology targets 4.2.1 PEMFC 4.2.1.1 Durability 4.2.1.2 Cost 4.2.1.3 Performance 4.2.2 Electrolysis 4.2.2.1 Main issues hampering the commercial diffusion of electrolysis 4.3 Main electrocatalyst aspects affecting design 4.3.1 Electrochemically Active Surface Area 4.3.2 Surface Defects, Surface structure and Particle Shape 4.3.3 Transport Issues 4.4 Constraints affecting design 4.4.1 Precious metal loading 4.4.2 Stability 4.4.3 Scale-up and manufacturing 4.5 The potential of nanotechnology in electrocatalyst design References PART 2. SUPPORT MATERIALS Chapter 5: Carbon based nanomaterials 5.1 Key concepts 5.2 Influence of the carbon support on the catalytic activity of metal nanoparticles 5.3. Carbon Blacks 5.3.1 Activation and functionalization of carbon blacks 5.4 Other carbon nanostructured materials 5.4.1 Mesoporous carbon 5.4.2 Carbon gels 5.4.3 Carbon nanotubes 5.4.4 Graphene References Chapter 6. Other Support Nanomaterials 6.1 Key Concepts 6.2 Inorganic oxides 6.2.1 Sub-stoichiometric titanium oxides 6.2.2 Stoichiometric titanium oxides 6.2.3 Metal doped titanium oxide 6.2.4 Tungsten Oxides 6.2.5 Other Oxides 6.3 Inorganic metal carbides and nitrides 6.3.1 WC 6.4.2 Other Carbides 6.4.3 Nitrides 6.5 Conductive polymers 6.6 Composite Materials References PART 3. ACTIVE MATERIALS Chapter 7: Supported metal nanoparticles 7.1 Key concepts 7.2 Metal nanoparticle synthetic techniques 7.2.1 Low temperature chemical precipitation 7.2.2 Impregnation 7.2.3 Colloidal 7.2.4 Microemulsions 7.2.5 Polyol method 7.2.6 Microwave assisted polyol 7.2.7 Electrodeposition 7.2.8 Pulse electrodeposition (PED) 7.2.9 Vapor phase methods 7.2.11 Sputter deposition technique 7.2.12 Sonochemistry and sonoelectrochemistry 7.2.13 Spray pyrolisis 7.2.14 Supercritical Fluids 7.2.14.1 Supercritical deposition technique 7.2.15 High Energy Ball Milling 7.3 Commercial supported nanoparticles for electrocatalysis References Chapter 8 Shape and structure controlled metal nanoparticles 8.1 Key concepts 8.2 Identification of High-Index Facets 8.3 Surface structure effects in electrocatalysis: 8.3.1 The oxidation of small organic molecules 8.3.2 Electrooxidation of CO 8.3.3 Oxygen Reduction 8.3.4 Effects of surface structure on selectivity in higher alcohol electrooxidation 8.4 Common strategies and synthetic methods 8.4.1 Small adsorbate-assisted facet control of Pt and Pd nanocrystals 8.4.1.1 Carbon monoxide 8.4.1.2 Halide anions. 8.4.1.3 Amines. 8.4.1.4 Formaldehyde. 8.4.2 Facet control by electrochemical methods 8.4.3 UPD 8.4.4 Kinetic Controlled Growth 8.4.5 Seeded growth 8.5 Other Pt and Pd morphologies with High-Index Facets 8.5.1 Pd, Au and Pt nanowire arrays 8.5.2 Bimetallic Platinum and Palladium based nanowires 8.5.3 Multiple Twinned Pt nanorods 8.5.4 Nanostructured thin film (NSTF) catalysts References Chapter 9: Monolayer decorated core shell and hollow nanoparticles 9.1 Key concepts 9.2 Core shell nanoparticles 9.3 Synthesis of platinum and platinum alloy shells 9.3.1 Underpotential deposition (UPD) 9.3.2 Electrochemical de-alloying 9.3.3 Annealing and stepwise chemical approaches 9.4 Non platinum metal shells 9.5 Hollow nanoparticles References Chapter 10: Molecular complexes in electrocatalysis for energy production and storage 10.1 Key concepts 10.2. Rhodium molecular catalysts for Organometallic Fuel Cells (OMFCs). 10.3 Bi-metallic Ni-Ru molecular complexes as electrocatalysts for PEMFCs. 10.4 Fe and Ni molecular catalysts for hydrogen production by electrocatalysis 10.5 Molecular catalysts for electrochemical and photoelectrochemical reduction of CO2 10.5.1 Macrocyclic complexes. 10.5.2 Metal bipyridine complexes 10.5.3 Metal phosphine complexes 10.5.4 Carbon monoxide dehydrogenases enzymes 10.5.5 Photo-Electro-Reduction of CO2 10.6 Molecular complexes for fuel cells cathodes 10.6.1 Cathodes based on transition metal complexes with phthalocyanine ligands 10.6.2 Transition metal complexes with porphyrin ligands 10.6.3 Carbon-supported metal chelates for ORR synthesized at high temperature References Chapter 11: Concluding Remarks 11.1 Summary 11.2 Considerations 11.3 Thinking outside of the box References

Improvement in the efficiency of an OrganoMetallic Fuel Cell by tuning the molecular architecture of the anode electrocatalyst and the nature of the carbon support

The electrooxidation of ethanol to acetate is achieved with Rh(I) diolefin amine complexes of the general formula [Rh(Y)(trop2NH)(L)] (L = PPh3, P(4-n-BuPh)3; Y = triflate, acetate; Bu = butyl) in direct alcohol fuel cells that have the peculiarity of containing a molecular anode electrocatalyst and, hence, are denoted as OrganoMetallic Fuel Cells (OMFCs). Changing the carbon black support from Vulcan XC-72 (Cv) to Ketjenblack EC 600JD (Ck) and/or the axial phosphane to produce non crystalline complexes has been found to remarkably change the electrochemical properties of the organorhodium catalysts, especially in terms of specific activity and durability. An in-depth study has shown that either Ck or P(4-n-butylPh)3 favour the formation of an amorphous Rh-acetato phase on the electrode, leading to a much more efficient and recyclable catalyst as compared to a crystalline Rh-acetate complex which is formed on Cv with PPh3 as the ligand. The ameliorating effect of the amorphous phase has been ascribed to its higher number of surface complex molecules as compared to the crystalline phase. A specific activity as high as 10 000 A gRh−1 has been found in a half cell, which is the highest value ever reported for ethanol electrooxidation.

Carbon supported Au–Pd core–shell nanoparticles for hydrogen production by alcohol electroreforming

Bimetallic nanoparticle catalysts generally exhibit enhanced activity and selectivity in electrocatalytic reactions as combining metals allows tuning of the electronic and surface structures. In this article, monodisperse faceted icosahedral Au–Pd core–shell nanocrystals of small size (<12 nm) supported on Vulcan XC-72 (Au–Pd/C) are investigated for hydrogen production by alcohol electroreforming. We investigate a range of renewable alcohols including diols, such as ethylene glycol, glycerol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol. Au–Pd/C shows selectivity for the partial oxidation of the diols to the corresponding mono-carboxylates. These include chemicals like lactate and glycolate that are important industrial intermediates. We have also investigated changes to the catalyst nanostructure under electrocatalytic conditions. Significantly, clustering of the NPs on the carbon support occurs without a negative effect on the activity. The palladium shell becomes elongated suggesting some migration of Pd from the shell occurring through alloy formation at the gold–palladium interface.

Energy and Chemicals from the Selective Electrooxidation of Renewable Diols by Organometallic Fuel Cells

Organometallic fuel cells catalyze the selective electrooxidation of renewable diols, simultaneously providing high power densities and chemicals of industrial importance. It is shown that the unique organometallic complex [Rh(OTf)(trop2NH)(PPh3)] employed as molecular active site in an anode of an OMFC selectively oxidizes a number of renewable diols, such as ethylene glycol , 1,2-propanediol (1,2-P), 1,3-propanediol (1,3-P), and 1,4-butanediol (1,4-B) to their corresponding mono-carboxylates. The electrochemical performance of this molecular catalyst is discussed, with the aim to achieve cogeneration of electricity and valuable chemicals in a highly selective electrooxidation from diol precursors.