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In recent years, air- and water-sensitive nanostructured materials with minimal surface oxide coverage have received increased attention for their potential role in various applications, such as catalysts for combustion fuels, active ingredients in solid-propellant rockets, and reactants for onboard and on-demand hydrogen generation to feed fuel cells. However, the fabrication of this class of materials has been hindered by their inherently high chemical reactivity. Magnesium, with its standard reduction potential of -2.37 V vs. SHE, is highly water-reactive in its nanostructured form, thus the synthesis of nanostructured magnesium with minimal surface oxide coverage poses a challenge. In this talk, I will introduce a novel eco-friendly air-free selective electrolytic leaching route to fabricate three-dimensional (3D) bicontinuous nanoporous magnesium (NP-Mg) with minimal surface oxide coverage. The starting material consists of a Mg-Li parent alloy, with lithium as the sacrificial component. During selective electrolytic leaching in an anhydrous lithium-conducting organic electrolyte solvent, the sacrificial lithium is stripped from the Mg-Li parent alloy used as the working electrode and plated on a pure lithium foil used as the counter electrode. This process enables sacrificial element recovery, making it eco-friendly. The dealloyed NP-Mg exhibits a characteristic ligament and pore size in the range of 20-30 nm, and its morphology was thoroughly investigated using electron microscopy, inductively coupled plasma (ICP) spectroscopy, small-angle X-ray scattering (SAXS), and X-ray diffraction, as will be shown during my talk. NP-Mg with such ultra-small feature size could be attractive for several applications including hydrogen storage in the form of magnesium hydride, and on-demand hydrogen generation by hydrolysis with pure water.

The increasing popularity of Li-ion batteries in new applications such as electric vehicles is expected to cause the key resources (Li, Ni and Co) used in these batteries to become scarce. Alternative battery technologies, including Mg-ion, Na-ion, and metal-air batteries are therefore desirable. In this talk, I will discuss the use of operando wide-angle X-ray scattering (WAXS) to study the crystalline to amorphous phase transformations that are key to the outstanding performance of state-of-the-art alloy-type Mg- and Na-ion anodes. The 1st part of the talk will be on the impact of the crystalline-to-amorphous transformation on batteries cycle life. Here I will discuss our novel self-healing Ga/Mg anode, which holds the current record for cycle performance and rate capability in alloy-type Mg-ion battery anodes, owing to a crystalline Mg2Ga5 to amorphous liquid Ga phase transformation occurring near room temperature, preventing the well-known pulverization issue in alloy-type anodes.[1] The 2nd part of the talk will detail the impact of the crystalline-to-amorphous transformation on the rate capabilities of batteries. Here, I will present our nanoporous Sb/Na system, which transforms from crystalline Na3Sb to crystalline Sb, going through an amorphous intermediate. It will be shown using a combination of WAXS, electrochemical characterization, and computational study based on ab initio grand canonical (aiGCMC) simulations that the amorphous intermediate phase favors high rate Na storage in Sb.[2] [1] Wang, L., Welborn, S. S., Kumar, H., Li, M., Wang, Z., Shenoy, V. B., Detsi, E.: High‐Rate and Long Cycle‐Life Alloy‐Type Magnesium‐Ion Battery Anode Enabled Through (De)magnesiation‐Induced Near‐Room‐Temperature Solid–Liquid Phase Transformation. Adv. Energy Mater. 2019, 1902086. https://doi.org/10.1002/aenm.201902086 [2] M. Li, T. Qiu, S. Welborn, A. Foucher, B. Lesel, E. Stach, A. M. Rappe, E. Detsi: Understanding the Fast Kinetics of Sodium Storage in Antimony (unpublished)

Effective hydrogen storage is still a challenge because the common approach to store hydrogen gas mechanically compressed in cylinders can be unsafe due to the high pressure and flammability risks involved. A promising alternative is solid-state hydrogen storage in lightweight materials. In this work, we explore ways to store hydrogen in ultrafine nanoporous aluminum during real-time fabrication of this nanoporous aluminum. Here I will present our novel scalable air-free synthesis method for ultrafine and oxide-free nanoporous aluminum with structure size in the range of 10-20 nm via selective electrolytic dealloying [1,2] and show how we extend this method to incorporate hydrogen in this nanoporous aluminum. Hydrogen can then be released by heating the material at moderate temperatures (~130°C). This method of hydrogen storage can find great use in on-board hydrogen storage for vehicular applications. [1] J.S. Corsi, J. Fu, Z. Wang, T. Lee, A. K. Ng, and E. Detsi: ACS Sustainable Chem. Eng. 7 (2019). [2] T. Lee, J. Fu, V. Basile, J. Corsi, Z. Wang, and E. Detsi: Under Review.

Charge storage in pseudocapacitive materials occurs through electron transfer (i.e. faradaic current) involving oxidation and reduction reactions. This process is usually extremely fast because the reactions take place near the surface of the material, meaning the species involved diffuse over short distances. Ionic species such as H+, OH-, Li+, and Na+ commonly used to store charge in pseudocapacitive materials are usually “foreign” elements in the materials. In this talk, I will demonstrate a pseudocapacitive charge storage approach where the ionic species is part of the material. Here we use Ag+ as the working ion in a non-aqueous electrode and silver (I) oxide grown on a three-dimensional nanoporous gold scaffold as the storage medium. Pseudocapacitive charge storage occurs through electrochemical oxidation/reduction of silver (I) oxide to silver (III) oxide at scan rates as high as 1000 mV/s. These high rates are justified by (i) the intrinsic nature of the working ion (Ag+), which is better accommodated by the host silver oxide material as opposed to foreign ions, and (ii) the excellent electronic conductivity provided by the 3D metallic scaffold current collector.

Thin films of nanoporous gold (NP-Au) have been extensively studied for localized surface plasmon resonance [1,2], showing a strong structure-property relationship between the morphology of the porous network and resonant frequencies. In this talk, I will show how we take advantage of this structure-property relationship and use UV-Visible optical spectroscopy to study the morphology evolution in NP-Au thin films in situ during selective electrolytic leaching of the sacrificial Ag from Au-Ag parent alloy. The evolution of plasmon resonance frequencies obtained from in situ UV-Vis spectra are directly linked to the morphology evolution (development of pores and changes in structure size) and the chemical composition (change in Ag content) in NP-Au, as confirmed by ex situ electron microscopy data. [1] A. Pröschel, J. Chacko, R. Whitaker, M. A. U Chen, and E. Detsi: Journal of The Electrochemical Society 166, H146-H150 (2019). [2] E. Detsi, M. Salverda, P.R. Onck and J.T.M. De Hosson: Journal of Applied Physics 115, 044308 (2014)

Over the past decade, tremendous progress has been made in transitioning from fossil fuel-based transportation to electric vehicles powered either by lithium-ion battery (LIB) or proton-exchange membrane (PEM) fuel cell technologies. A hybrid fuel cell-battery power generation system is more attractive than a battery alone, or a fuel cell alone, since a battery is able to meet the high-power requirements during peak demands (e.g. acceleration), while a fuel cell can be used as a range extender. Existing hybrid PEM fuel cell-battery power generation systems consist of separate LIB and PEM fuel cell systems that are coupled together. In this configuration, the hydrogen used to feed the PEM fuel cell is stored on-board in high-pressure tank. In this talk, I will present our novel integrated hybrid PEM fuel cell-battery power generation system, which can simultaneously produce both electricity, acting as a battery, and hydrogen gas, which is then used to directly feed a PEM fuel cell, from a single device. We have previously reported the scalable synthesis of novel bulk nearly oxide-free nanoporous aluminum (NP-Al) and the ability to produce hydrogen gas through “chemical” hydrolysis of NP-Al in pure water, with solid aluminum hydroxide, hydrogen gas and heat as the only reaction products. [1] The new hybrid power system proposed here builds on this work through the introduction of a novel cell configuration which facilitates the spontaneous “electrochemical” hydrolysis of NP-Al, during which aluminum is oxidized at the anode, electrons from this oxidation reaction diffuse through an external circuit to the cathode where hydrogen evolution takes place, meanwhile electricity is also generated from electrons flowing through the external circuit. This electricity is the equivalent of the heat generated during chemical hydrolysis reaction, meaning that during electrochemical hydrolysis, the only reaction products in case of 100 % reaction efficiency are solid aluminum hydroxide, hydrogen gas and electricity without heat. In this talk, I will discuss this novel cell, current progress and outlook for future development. Reference: [1] Corsi JS, Fu J, Wang Z, Lee T, Ng AK, Detsi E. (2019). Hierarchical Bulk Nanoporous Aluminum for On-Site Generation of Hydrogen by Hydrolysis in Pure Water and Combustion of Solid Fuels. ACS Sustainable Chemistry and Engineering, 7, 11194–11204. doi.org/10.1021/acssuschemeng.9b00481

Jules Verne stated more than 145 years ago that water will be the coal of the future [1]. Indeed, hydrogen, a highly abundant substance on Earth in the form of water, is a promising energy carrier for producing zero-emission electricity upon reaction with oxygen using fuel cell technology. There are still many scientific and engineering challenges that need to be addressed before Jules Verne’s dream can become true, however. Two of these challenges include hydrogen production from water and hydrogen storage. In this talk, I will present our work on direct hydrogen generation by hydrolysis of nanoporous aluminum in pure water to feed a 2.4 kW PEM fuel cell stack, which in turn can be used to power a low speed electric vehicle. The possibility to make nanoporous aluminum from secondary aluminum and the advent of carbon-free primary aluminum from Elysis [2,3] could make hydrogen production by hydrolysis of aluminum with pure water a promising alternative to hydrogen production by electrolysis of water. References: [1] Ryabchuk, V. K., Kuznetsov, V. N., Emeline, A. V., Artem’ev, Y. M., Kataeva, G. V., Horikoshi, S., & Serpone, N. (2016). Waterwill be the coal of the future-the untamed dream of Jules Verne for a solar fuel. Molecules, 21(12), 1–20. https://doi.org/10.3390/molecules21121638 [2] Corsi, J. S., Fu, J., Wang, Z., Lee, T., Ng, A. K., & Detsi, E. (2019). Hierarchical Bulk Nanoporous Aluminum for On-Site Generation of Hydrogen by Hydrolysis in Pure Water and Combustion of Solid Fuels. ACS Sustainable Chemistry and Engineering, 7, 11194–11204. https://doi.org/10.1021/acssuschemeng.9b00481 [3] ELYSIS. Retrieved from https://www.alcoa.com/global/en/what-we-do/elysis/.

Recently, sodium-ion batteries (SIB) have been considered a promising alternative to lithium-ion batteries due to the abundance of sodium resources (sodium is the Earth’s 6th most abundant element, while lithium is 33rd) and its low extraction costs. Among various cathode candidates, the layered oxides NaTMO2 (TM=3d transition metal elements and their mixture) can accommodate sodium ions through intercalation mechanism, but suffer from major limitations including poor rate capability and short cycle-life. We have developed a novel bulk Na2/3[Ni1/3Mn2/3]O2 structure containing inclusions, which exhibits an unprecedented rate capability with roughly 50 % capacity retention at 50 C, and a remarkable long-term cycling stability with 95% capacity retention after 1000 cycles at 5 C. During this talk, I will present our new results and elucidate the mechanism through which the cycling performance of the novel materials system is enhanced. References Ruiz, M. Cochrane, M. Li, Y. Yan, K. Ma, J. Fu, Z. Wang, SH. Tolbert, VB. Shenoy, E. Detsi, Adv. Energy. Mater., 8 (2018) 1801781. Li, Z. Wang, J. Fu, K. Ma, E. Detsi, Scripta Materialia, 164 (2019) 52-56.

A large amount of literature exists on the electrochemical characterization of various high capacity sodium-ion battery electrodes; however, their mechanical behavior has not been characterized before. In this study, evolution of stress in sodium-ion battery electrode has been measured in real-time using an optical-based substrate curvature measurement apparatus. A 100 nm Ge thin film, as working electrode, was cycled against sodium reference/counter electrode with 1 M sodium perchlorate (NaClO4) in propylene carbonate (PC) as electrolyte. Electrochemical and stress response of the electrodes to the prescribed electrochemical cycling conditions were measured simultaneously. Further, the sodiated Ge samples were analyzed using SEM, XRD, and AFM techniques to understand the microstructural changes. It was observed that sodiation of Ge films resulted in distinctly different mechanics and electrochemical phenomenon compared to that of lithiated Ge films. These observations and implications will be further discussed in the talk.

Despite the remarkable key features of hydrogen energy technology such as the high gravimetric energy density of hydrogen, the zero-emissions electricity generated using fuel cells, and the high natural abundance of hydrogen resources (particularly in the form of water), there are still many scientific and engineering challenges that must be addressed before a true sustainable hydrogen economy can be realized. Two of these challenges include sustainable hydrogen generation without CO2 emissions and effective storage of this hydrogen for specific applications. In this presentation, I will present a sustainable method to produce hydrogen on-board, which could be used to overcome the two challenges mentioned above. Our approach involves: (i) Fabrication by selective alloy corrosion of hierarchical bulk nanoporous aluminum characterized by the coexistence of both macroscopic and mesoscopic ligament/pore structures, with the mesoscopic ligaments in the range of 10-20 nm. (ii) Recovery of the sacrificial material simultaneously during selective alloy corrosion, which contributes to sustainability of the process. (iii) Use of this hierarchical bulk nanoporous aluminum to produce hydrogen and heat on-board by hydrolysis with “pure” water, with a yield of ~52-85 % during hydrogen production without incorporation of any catalyst or reaction promoter in the aluminum-water system. Besides hydrogen and heat generations, I will demonstrate the combustion of this bulk nanoporous aluminum in air and under ambient conditions, which implies that this material could be attractive as a combustion fuel catalyst, e.g. to enhance the ignition and combustion of solid propellants. Thanks to a new carbon-free sustainable pathway to extract aluminum by Elysis (https://elysis.com/en), a joint venture composed of high-profile aluminum suppliers including Rio Tinto and Alcoa, and aluminum consumers including Apple, aluminum can be obtained by electrolysis of Al2O3 without CO2 emissions. The inclusion of this carbon-free aluminum in our process will make it possible to produce hydrogen from nanoporous aluminum and pure water without greenhouse gas emissions at any stage of the process.

The growing popularity of lithium-ion batteries has raised a serious concern about the long-term supply of these batteries, since lithium and cobalt resources used are becoming more expensive due to demand, and the global cobalt market heavily depends on the supply from countries with high geopolitical risks. Therefore, scalable alternatives battery technologies are desirable to reduce the dependence on lithium and cobalt. Over the past few years, magnesium-ion batteries have been the subject of intense research as an alternative to lithium, owing to the various advantages of magnesium including the abundance of magnesium resources for large-scale applications. Nevertheless, progress toward practical magnesium-ion batteries has been impeded, partly by the absence of suitable electrolytes that are compatible with magnesium metal used as the negative electrode. Typically, common salts and organic solvents combinations similar to those used in lithium-ion batteries yield a magnesium-ion-blocking passive film on the magnesium metal negative electrode. A promising way to circumvent this electrolyte issue is through the use of alloy-type anodes as the negative electrode instead of magnesium metal. However, state-of-the-art alloy-type magnesium-ion battery anodes can only be reversibly cycled up to 200 times with acceptable capacity retention [1]. Such a cycle-life is far below the thousands of cycles required for practical battery applications. In this talk, I will present a novel high-performance alloy-type magnesium-ion battery anode which we have developed, which can be reversibly (de)magnesiated at the C-rate of 3C over 1000 cycles with excellent capacity retention. This exceptional performance is to thanks to the self-healing property of the active electrode material, which undergo solid-to-liquid phase transition when the cell operate around 30-40oC. Operando X-ray scattering techniques were used to demonstrate this self-healing property in real-time during magnesiation and demagnesiation. Keywords: Mg-ion battery anode, self-healing, operando X-ray scattering, solid-liquid phase transition [1] CHENG, Y., et al. 2015. Interface promoted reversible mg insertion in nanostructured tin-antimony alloys Adv. Mater. 27, 6598-6605.

Nanostructured Sn as negative electrode material in Mg-ion batteries suffers from very slow magnesiation kinetics when its nanoscale feature sizes are not in the sub-100 nm range. Herein, we use electrochemical experiments in combination finite element modeling (FEM) to demonstrate a cost-effective route to nanostructured Sn for high performance Mg-ion battery anodes. Using FEM we found that antagonistic stresses developed during dealloying of Mg2Sn induce pulverization of the dealloyed material and formation of nanostructured Sn with characteristic feature size in the sub-100 nm range. These results were further confirmed through electrochemical experiments using a Mg half-cell consisting of bulk Mg2Sn particles with average characteristic size larger than 10 μm as the working electrode, cycled versus Mg metal as counter and reference electrodes, and all-phenyl complex (APC) electrolyte. Ex situ electron microscopy and diffraction techniques were used to study the working electrode material in the pristine, demagnesiated and re-magnesiated forms. The results suggest that the starting micrometer-sized Mg2Sn particles are converted into nanostructured β-Sn with characteristic sizes ranging from 10‒50 nm during the first demagnesiation. Electrochemical performance of the in situ formed nanostructured Sn was further investigated during subsequent (de)magnesiation cycles in combination with electrochemical impedance spectroscopy (EIS). EIS studies suggest the formation of passive films on the Mg2Sn electrode. A reversible capacity of 300 mAh/g was demonstrated over 150 cycles at the rate of C/5 after application of a combined sequence of regular galvanostatic cycling with an oxidative pulse to control the passive film formation. This work is expected to open new avenues for cost-effective routes to high performance alloy-type Mg-ion battery anodes without complex nanosynthesis steps.