Nanostructured Materials for Next-Generation Energy Storage and Conversion

When Dwight D. Eisenhower became the 34th president of the United States, he was the first incumbent of the office that did not hold any political office within state government or within the US Congress, excluding military service, since Ulysses Grant. No president prior to or since has crafted and influenced energy policy to the degree of President Eisenhower. As the first officeholder without a past “congressional” career, he was viewed as pro-business and pro-military, and the expectations of his government were that nuclear energy would provide cheaper electricity. The challenges during his administration enabled him to adopt a more orthodox policy stance, and the nuclear energy policies did not proceed as anticipated or planned. The 45th President of the United States, Donald Trump, is the only individual since Eisenhower without a prior congressional-type political career. Since he has a foundation in real estate business, like Eisenhower, he is perceived as “pro-business,” and it is pertinent to compare similar energy policies under the current administration. Although the current administration is only 100 days old, statements during the primaries, general election, and first 100 days in office and first proposed federal budget suggest that tax credits for electric vehicles and other tax assistance credits will be discontinued and that certain brackets of taxes will be eliminated or greatly reduced. And many federal policies enacted under the Obama administration related to environment and energy will be rolled back, favoring coal, drilling, and Keystone XL and the Dakota Access Pipelines. Whether these policies will promote domestic energy production, reduce the import-to-export gap, or lower the “energy deficiency” is too early to gauge. The introduction of potential import fees or border taxes may promote coal extraction at the expense of natural gas exploration. This may also impact gasoline prices at the pump since crude oil imported from other countries would have taxes or fees levied on it. Coupled with limiting environmental regulations and capping liabilities, lower corporate tax rates for oil exploration companies may promote domestic energy production, because of lower operating costs and liabilities, and may increase corporate profits, although these trends may not be observable within the lifetime of the first term of President Trump. In addition, the projected 3% growth in employment over the current 1.7% is again too early to discern, although most economist’s opinions are that these targets will not be met since these currently are proposals and not implemented policy.

The purpose of this paper is to review the hydrogen redox electric power and hydrogen generation systems (HREG). It offers considerable conceptual advantage such that it functions with zero energy input, zero matter input, and zero emission without violating the laws of thermodynamics. Its application ranges from the large-scale central station power generation down to the small-scale onboard power generation system for electric vehicles with infinite cruising range. The hydrogen redox hydrogen generator also works with zero power input. To attain a highly positive energy balance, the advantage was taken of the electrostatic energy that appears in the water electrolysis when a constant static voltage is applied across parallel electrodes. A feature and an essential part of these generators are then the electrostatic-to-chemical energy conversion in the water electrolysis. The method proposed here for supplying energy to the electrolytic cell, which has been termed electrostatic-induction potential-superposed electrolysis (ESI-PSE), theoretically reduces the power requirement for water electrolysis down to 17% of the total energy required. If the ESI-PSE electrolyzer, which delivers pure stoichiometric H₂-O₂ fuel for a fuel cell, is combined with a fuel cell to form an energy cycle, then this may lead to the concepts of hydrogen redox electric power and hydrogen energy generators. According to the calculations using the data of operational conditions for the commercial electrolyzers and fuel cells, more than 70% of the power delivered from the fuel cell can be extracted outside the cycle as net power output. Because of the simplicity, effectiveness, cleanliness, and self-exciting, these novel generators may offer a potential route for its practical application to the electricity and hydrogen production systems of the future. In addition, attempts were made to examine the possibilities of the onboard HREG system for an infinite cruising range of regular passenger cars.

We summarized investigations on the evaluation of cell performance and durability for cathode catalysts on two types of supports, carbon blacks (CBs) and conducting ceramic nanoparticles, during simulated fuel cell vehicle (FCV) operation, including start-up/shutdown (SU/SD) cycles and load cycles. In cathode catalyst layers (CLs) using Pt supported on CBs (Pt/CBs), the effects of graphitized CB (GCB) and Pt nanoparticle size, as well as its dispersion state on the GCB, were investigated on both the performance and durability. The negative effects of the interim cyclic voltammetric measurements on the Pt/CB catalyst degradation during SU/SD cycling evaluation, which led to an overestimation of the degradation process, were also suggested. We found that catalyst degradation occurred not only in the outlet region but also in the inlet region during the gas-exchange SU. Degradation of CBs during a hydrogen passivation SU/SD process was found to decrease but still to occur, due to local cells arising from nonuniform distributions of ionomer and Pt particles. The effects of load cycle conditions, which involved open circuit and load holding times, and variations of current density, and humidity, on the durability of the cathode were also investigated. The buildup of Pt oxides at higher potentials during open circuit and re-reduction at lower potentials during high current density operation led to accelerated degradation; these conditions have relevance to ordinary operation with drastic load changes. For the intrinsic improvement of SU/SD durability, we synthesized conducting ceramic nanoparticles. The durability of the cathode CLs, using Pt supported on conducting ceramic nanoparticles with a fused-aggregate network structure, was superior to that of Pt/GCB. We also proposed that the cathode CL degradation can be mitigated by the use of ceramic nanoparticles in the anode because of the significant reduction of the reverse current due to the high resistivity in the air, termed the “atmospheric resistive switching mechanism” (ARSM).

New mono- and polymetallic electrocatalysts were synthesized from the carbonyl cluster compounds through thermolysis and pyrolysis methods. The precursor compounds used were triosmium dodecacarbonyl [Os₃(CO)₁₂], triruthenium dodecacarbonyl [Ru₃(CO)₁₂], tetrairidium dodecacarbonyl [Ir₄(CO)₁₂], and hexarhodium hexadecacarbonyl [Rh₆(CO)₁₆]. In the syntheses by thermolysis, the reaction time (between 5 and 20 h) and the temperature were modified as a function of the solvent used (dimethyl sulfoxide, o-dichlorobenzene, n-nonane, and o-xylene). The pyrolysis variables, including the temperature (90–500 °C), atmosphere gases (nitrogen and hydrogen), and reaction time (controlled at 5 h), were optimized. The precursor compounds and final products were structurally and morphologically characterized using spectroscopic and microscopic analyses. It was found that some of the products showed a metallic character and others were more nonmetallic due to the incorporation of carbonyl groups in their structures. The oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) were measured to evaluate the electrochemical performance of these synthesized electrocatalysts, in the absence and presence of methanol and carbon monoxide, respectively (both contaminants in different concentrations). The materials were tested by rotating disk electrode (RDE), cyclic voltammetry (CV), and linear sweep voltammetry (LSV).

The electrochemical analyses indicated that majority of the electrocatalysts exhibit a dual electrocatalytic behavior toward ORR and HOR. These catalysts are also tolerant to methanol and carbon monoxide, respectively. The synthesized catalysts have superior performance relative to commercial platinum catalysts, which are easily poisoned by CO (ppm). Some iridium-based materials were found to be able to oxidize methanol and ethanol, although their catalytic activity remains to be improved. The most kinetically active catalysts were incorporated into a proton exchange membrane fuel cells (PEMFCs), as part of a Research and Advanced Studies Center, Campus Querétaro (CINVESTAV-Querétaro) fuel cell test system. Under different cell operating conditions, electrical power was generated sufficiently to drive appliances even when a fuel mixture of H₂/0.5% CO was introduced. This design opens a new paradigm to apply reforming hydrogen into PEMFCs, with a reduced manufacturing costs and energy balance. The other advantage of this approach is the tolerance of the electrocatalyst to CO, which can poison traditional platinum-based catalysts.

To improve electrochemical performance of the fuel cell devices, various nanoscaled materials were produced using different methods such as colloidal chemistry, physical deposition, pyrolysis, and solid-state chemistry. Series of materials such as Pt-catalytic support materials are described and include doped metal oxides, carbides, nitrides, borides, mesoporous silica, metal, and conducting polymer-based support materials for Pt class of electrocatalysts. In this chapter, we summarized the recent developments in the advanced synthesis of electrodes for low-temperature fuel cells, cathode, and anode catalyst for proton exchange membrane fuel cells (PEMFCs). The structures of these materials were highly diversified, including core-shell, hybrid catalytic materials, and skinned-shell structures. We also discuss tolerance to acidic media and CO of catalysts supported by metal and mixed metal oxide nanocatalysts with mesoporous, hollow, or multilayered structures. Their representative catalytic applications in the fuel cell devices particularly in oxygen reduction reaction (ORR), hydrogen oxidation reactions (HOR), and methanol oxidation reaction (MOR) are discussed. We highlighted perspectives for their challenges ahead and opportunities for their use in low-temperature fuel cells and PEMFCs. Based on the structural characterization and performance of the devices, we further listed the ideal support material characteristics to enhance the stability and durability of these carbon-based and non-carbon-based support materials for Pt and non-Pt nanocatalysts used in low-temperature fuel cells.

The chapter begins with a brief introduction of the importance and role of electrocatalysts in fuel cells. The following sections discuss the current state-of-the-art for noble metal electrocatalysts in polymer electrolyte fuel cells (PEFCs) along with an examination of recent developments in various noble metal (Pt, Pd, Au, Ag, Ir, Ru) electrocatalysts used in anode and cathode of a PEFC. Various 0D, 1D, 2D, and 3D nanostructured morphologies of electrocatalysts are scrutinized. Different factors responsible for influencing and manipulating the electrocatalytic response and the stability of electrocatalysts are also discussed. The need and scope for recycling of precious metal electrocatalysts are examined and finally expected future trends are deliberated.

With the rapid development of modern science and technology in the current society, environmental conservation and taking advantage of new energy sources have become the core strategies of sustainable development for society. Micro-energy technology has boasted a huge potential in market demand and attracted a great deal of interest in research and development since it is safe, efficient, and environmentally friendly and meets the goals for portable devices on the exterior, weight, and endurance. Although significant advancements have been achieved for proton exchange membrane fuel cells (PEMFCs) in recent years, PEMFCs still suffer from the key problems of low power density and fuel utilization, which are related, respectively, to poor reaction kinetics and methanol permeation through the membrane (viz., methanol crossover). Nanomaterials recently have attracted lots of attention owing to their distinguishing physical and chemical characteristics. Among them, carbon-based nanostructured materials such as graphene (G) and carbon nanotube (CNTs) have been successfully applied in fuel cells. PEMFC combined with nanostructured materials has remarkable improvements compared with the traditional fuel cells.

Solid oxide fuel cell (SOFC) is an all-solid-state ceramic electrochemical device for converting chemical energy (fuels) to electricity with high energy efficiency and ultralow harmful emissions. These classes of FCs have received significant attention by researchers as a potential replacement for petroleum-based energy devices. In order to broaden the material selection and increase material system durability, the development of intermediate- or low-temperature SOFC is critical to making their commercialization viable. Therefore, the SOFC performance at lowered operating temperatures must be improved by the innovation of materials and microstructures. The nanostructure engineering of electrodes has demonstrated their improved catalytic performance due to minimization of the electrode polarization resistances for oxygen reduction reaction and fuel oxidation reaction at the nanoscale compared to the traditional electrode design. The synthesis technique strategy was based on wet chemistry catalyst infiltration into electrode structure and has been demonstrated improvements in power density and electrode stability. In this chapter, the technical process of ion infiltration method is discussed; and the different routes in fabricating nanostructured electrodes to achieve high-performing SOFC in hydrogen and hydrocarbon fuels are reviewed. The electrode parameters that lead to improvement of SOFC performance are also summarized. By fabricating electrodes at the nanoscale, a significant increase in specific area was obtained that can provide greater active catalysis sites for electrode reactions, as well as a decrease in the activation polarization resistance which collectively led to improved SOFC performance.

The performance degradation of proton exchange membrane or polymer electrolyte membrane fuel cell (PEMFC) stems from air starvation and water flooding. In the mathematical modeling, the conservation equations were applied for momentum, mass, species, charge, and energy, to investigate the heat transfer and temperature distribution in the cathode along with the multiphase and multi-species transport under the steady-state condition. This model shows the effect of stoichiometry of reactants and relative humidity on the water saturation. The back-diffusion of water from the cathode to the anode is considered to reduce possible flooding. The feedback controls are used to address the transient water, pressure, and temperature management problems of a PEMFC system. An anode recirculation system measures the feedback signals to regulate the anode and cathode humidities and the pressure difference between the anode and cathode compartments. It was found that the robust nonlinear controller is insensitive to parametric uncertainty, maintaining performance around any equilibrium point.

The fundamentals of solid oxide fuel cell (SOFC) and computational thermodynamics, using the CALPHAD (CALculation of PHAse Diagrams) approach, are reviewed in this chapter. The thermodynamic database development for perovskites and fluorites is especially discussed. In addition, the application of computational thermodynamics to the cathode and electrolyte of SOFC is also discussed in detail including the defect chemistry and quantitative Brouwer diagrams, electronic and ionic conductivity, cathode-electrolyte triple phase boundary (TPB) stability, thermomechanical properties of perovskite cathode, the effect of gas impurities like CO₂ to the phase stability of cathode, and phase diagram development for nano (n-)yttria-stabilized zirconia (YSZ) particles.

Proton exchange membrane fuel cells (PEMFCs) are considered one of the most promising energy conversion devices due to their high-energy yield and low environmental impact of hydrogen oxidation. The oxygen reduction reaction (ORR) at cathode plays a crucial role during operation of the PEMFCs. However, for various classes of ORR catalysts, the detailed mechanism and the origin of activities require an in-depth understanding. This chapter focuses on the application of density functional theory (DFT) methods in investigating the activity and stability of ORR electrocatalysts to advance the PEMFC performance. The authors systematically reviewed the descriptors to evaluate the catalyst activity, such as adsorption properties of ORR intermediates, potential energy surfaces, reversible potentials, reaction barriers, and catalyst electronic structures. They also discussed various methods implemented to evaluate the ORR stabilities, such as metal dissolution potentials, metal cohesive energies, and binding energies of metal in the active sites.

The transformation of mobility is now beginning through the introduction of hydrogen (H₂) as an energy carrier, coupled with fuel cell electric vehicles that can utilize H₂ without greenhouse gas emissions. A current disadvantage of these vehicles lies in the limited infrastructure in terms of H₂ refill or electric recharge stations, which has hindered their widespread applicability. There is a sense of déjà vu in the current development in automobile design between battery electric and fuel cell vehicle. This race is similar to a competition when the internal combustion engine-driven Ford Model T automobile became the dominant transportation platform in displacing battery and steam-driven automobiles in the United States a century ago and opened up a new industry. In this chapter, we propose a change in the architecture of the power plant of the fuel cell and battery electric vehicles. The objective is that these vehicles can be presently used until the development of an electric and/or hydrogen recharge network allows both being useful with the current status. We present a drivetrain set model, which is a combination of a plugged-in battery and a fuel cell that works as a range-extender system. Different strategies are applied in order to determine the working conditions that will lead to better vehicle performance and higher range. The vehicle performance is referred to the capacity of both energy sources, namely, electricity stored in a lithium-ion battery and hydrogen gas in high-pressure storage tanks. –The possibilities presented in the chapter may open the door to strategic advantages and innovation for car designers in the future.

The totalized hydrogen energy utilization system (THEUS) proposed here is a hydrogen-based energy system originally designed to have both functions of load leveling and cogeneration in commercial buildings. In addition, THEUS has the potential to capture fluctuating energy input from renewable energy sources such as solar photovoltaics (PVs) and wind power. The main components of THEUS are a unitized reversible fuel cell (URFC) and metal hydride tank (MHT). In this chapter, first, the performances of URFC and MHT were verified individually. Then, a 3-day continuous operation of THEUS was evaluated. Finally, the potential of THEUS for capturing fluctuating energy input was verified experimentally. These experimental results clearly indicate the promising potential of THEUS as an innovative energy facility in stationary applications.

This chapter provides an overview of proton exchange membrane fuel cell (PEMFC) performance issues that stem from exposure to airborne pollutants. The PEMFCs must adapt to various functional environments and operate within well-established air quality thresholds in order to become commercially viable. Ambient air is the most convenient oxidant for PEMFCs; however, it may contain various contaminants that can cause significant performance loss in these energy conversion systems. The discussion focuses on the effects of organic and inorganic impurities on nanostructured electrocatalysts, such as Pt and novel material alternatives. This chapter compares different contamination mechanisms, electrochemically driven impurity evolution and transformation on catalyst nanoparticles, and the effects of these processes on the oxygen reduction reaction and PEMFCs’ subsequent performance. Finally, the chapter highlights possible PEMFC performance recovery and contaminant mitigation strategies. The discussion presents an overview of the experimental and computational approaches and efforts to reconcile observed performance with phenomenological modeling.

Hydrogen (H₂) is a promising replacement energy carrier and storage molecular due to its high energy density by weight. For the constraint of size and weight in vehicles, the onboard hydrogen storage system has to be small and lightweight. Therefore, a lot of research is devoted to finding an efficient method of hydrogen storage based on both mechanical compression and sorption on solid-state materials. An overview of the current research trend and perspectives on materials-based hydrogen storage including both physical and chemical storage is provided in the present paper. Part of this chapter was dedicated to recent results on two innovative materials: hybrid materials based on manganese oxide anchored to a polymeric matrix and natural volcanic powders. A prototype H₂ tank, filled with the developed hybrid material, was realized and integrated into a polymer electrolyte membrane (PEM) single fuel cell (FC) demonstrating the material capability to coupling with the FC.

The even distribution of mechanical stress along the fuel cell is an important metric to observe in order to preserve the integrity of the system’s components. The diversity of the fuel cell’s comprising materials and dimensions, ranging from thin polymers, porous electrocatalyst and gas diffusion layers, graphite blocks, gaskets, and seals to metallic foils and plates, produces different load transmission patterns. These variations in load when combined with their particular mechanical properties may promote localized stresses deriving in accelerated degradation or, even worse, in early unsafe failure.

In transport applications, main fuel cell mechanical stressors, such as the fuel cell assembly torque, operational parameters, and vibration, can induce harsh conditions altering the lifetime of the system. The ionomeric membrane and bipolar plates are critical components in the fuel cell that may fail through mechanical means; therefore, understanding their limitations to withstand mechanical stress is important in redesigning these components to prevent unintended damage and failure.

In this chapter, we give a personal perspective account of the mechanical properties of the fuel cell’s most sensitive components, i.e., the proton exchange membrane (PEM) and the bipolar plate (BP) are examined in the scope of their current material limitations; alternative material’s substitution is discussed for improving the endurance of the integrated fuel cell device. This chapter is designed to give the fuel cell practitioner real hands-on experience on the actual engineering aspects of FC bench testing and associated testing specifications including US Department of Energy guidelines and targets.

This chapter describes the method of producing hollow fiber for a microtubular solid oxide fuel cell (MT-SOFC) using nanomaterial-based structures. This chapter focuses on the utilization of yttrium-stabilized zirconia (YSZ) and cerium-gadolinium oxide (CGO) nanomaterials for high and intermediate working temperatures of MT-SOFC, respectively. The chapter then discusses the nanomaterial available and a number of attempts to produce the nanomaterial for the electrolyte. Then, the advantages of using nanomaterial are also discussed. Finally, this chapter concludes the future of nanomaterial for MT-SOFC and its future challenges.

The global demand for electricity has gradually increased to 20,000 TWh in 2016 at approximately 2% per decade. The top four resources to generate electricity are coal, natural gas, nuclear, and renewables. In the USA, natural gas has displaced coal as the primary source for the generation of electricity. In the transport sector, fossil fuels dominate. The two major drawbacks of using fossil fuels for energy and transport are the harmful emission of oxides of carbon, nitrogen, and sulfur and the limited availability of these resources if measured in centuries rather than years. To offset these short- and long-term problems, researchers have proposed the development of fuel cells (FCs) as a potential solution. The FCs convert fuels (such as hydrogen) into water and electricity with zero or near-zero emission of harmful gases. Hydrogen is generated using either water splitting or steam reformation of methane, coal gasification, or from methanol. The above alternative solutions require chemical and electrical energy and are not necessarily carbon dioxide neutral. To improve the efficiency and lower the cost of the fuel cell stack, researchers have focused on replacement of platinum anode/cathodes with other non-precious metals. Their potential toxicity and interactions with the environment, animals, and people have received little attention, unlike our understanding of the toxicity of gasoline volatiles, particulate matter, and organic residues. In this study, we evaluated the potential biological effects using core-shelled Fe₃O₄ magnetic nanoparticles (MNPs) as an example. The toxicity results indicate that electrocatalyst with appropriate structural support may be biologically benign. The toxicity of these catalysts may be an issue in the near future since the number of electric and hydrogen-powered automobiles with fuel cells is expected to increase. This increased utilization will lower consumption of fossil fuels, as well as emission of greenhouses gases, but will increase a secondary risk of the effects of these electrocatalysts. Our results demonstrate the minimization of oxidative stress and cellular damage if encapsulated with natural product extracts.