Numerous benefits of porous electrode materials for lithium ion batteries (LIBs) have been demonstrated, including examples of higher rate capabilities, better cycle lives, and sometimes greater gravimetric capacities at a given rate compared to nonporous bulk materials. These properties promise advantages of porous electrode materials for LIBs in electric and hybrid electric vehicles, portable electronic devices, and stationary electrical energy storage. This review highlights methods of synthesizing porous electrode materials by templating and template-free methods and discusses how the structural features of porous electrodes influence their electrochemical properties. A section on electrochemical properties of porous electrodes provides examples that illustrate the influence of pore and wall architecture and interconnectivity, surface area, particle morphology, and nanocomposite formation on the utilization of the electrode materials, specific capacities, rate capabilities, and structural stability during lithiation and delithiation processes. Recent applications of porous solids as components for three-dimensionally interpenetrating battery architectures are also described.

Porous Electrode Materials for Lithium‐Ion Batteries – How to Prepare Them and What Makes Them Special

Microbatteries offer new opportunities for microelectronics, but performance and integration remain a challenge. Pikul et al. develop a lithium ion microbattery with fully integrated nanoporous electrodes, which exceeds the power densities of most supercapacitors while retaining high-energy density.

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High-power lithium ion microbatteries from interdigitated three-dimensional bicontinuous nanoporous electrodes

Ordered mesoporous materials prepared by the template route have attracted increasing interest from the electrochemists community due to their plenty of unique properties and functionalities that can be effectively exploited in electrochemical devices. This review will cover the whole field of the intersection between electrochemistry and ordered mesoporous materials. The latter are either electronically insulating (silica and some other metal oxides, as well as silica-based organic–inorganic hybrid materials), semi-conducting (metal oxides), or conducting (metals, carbons). The three main intersection areas are: (1) the development/use of electrochemical methods to characterize the properties of mesoporous materials (i.e., charge and mass transfer processes); (2) the generation of mesostructured solids by electro-assisted deposition using appropriate templates; and (3) the application of these novel materials for electrochemical purposes. The most common devices to date are based on a bulk composite or thin film configuration and the resulting electrodes modified with such mesoporous materials have been successfully applied in various fields, including mainly electrochemical sensing and biosensing as well as energy conversion and storage (620 references).

Mesoporous materials and electrochemistry

Mesoporous non-siliceous oxides have attracted great interest due to their unique properties and potential applications. Since the discovery of mesoporous silicates in 1990s, organic–inorganic assembly processes by using surfactants or block copolymers as soft templates have been considered as a feasible path for creating mesopores in metal oxides. However, the harsh sol–gel conditions and low thermal stabilities have limited the expansion of this method to various metal oxide species. Nanocasting, using ordered mesoporous silica or carbon as a hard template, has provided possibilities for preparing novel mesoporous materials with new structures, compositions and high thermal stabilities. This review concerns the synthesis, composition, and parameter control of mesoporous non-siliceous oxides. Four synthesis routes, i.e. soft-templating (surfactants or block copolymers as templates), hard-templating (mesoporous silicas or carbons as sacrificial templates), colloidal crystal templating (3-D ordered colloidal particles as a template), and super lattice routes, are summarized in this review. Mesoporous metal oxides with different compositions have different properties. Non-siliceous mesoporous oxides are comprehensively described, including a discussion of constituting elements, synthesis, and structures. General aspects concerning pore size control, atomic scale crystallinity, and phase control are also reviewed.

Synthesis of non-siliceous mesoporous oxides

Templating with colloidal crystals composed of monodisperse spheres is a convenient chemical method to obtain porous materials with well-ordered periodicity and interconnected pore systems. The three-dimensionally ordered macroporous (3DOM) products or inverse opals are of interest for numerous applications, both for the optical properties related to structural color of these photonic crystal materials and because of their bicontinuous nanostructure, i.e., a continuous nanostructured skeleton with large interfacial area and a three-dimensionally interconnected pore system with low tortuosity. This review outlines various synthetic methods used to control the morphology of 3DOM materials with different compositions. It highlights aspects of the choice of colloidal particles, assembly of the colloidal crystal template, infiltration and processing, template removal, and other necessary modifications to enhance the functionality of the materials. It also considers syntheses within the confinement of 3DOM materials and summarizes characterization methods that are particularly useful in the analysis of 3DOM materials. The review then discusses chemical applications of 3DOM materials, namely sorption and controlled release, optical and electrochemical sensors, solar cells, lithium ion batteries, supercapacitors, fuel cells, and environmental and chemical fuel catalysis. A focus is on structural features and materials properties that enable these applications.

Design and functionality of colloidal-crystal-templated materials—chemical applications of inverse opals

Herein is reported the synthesis of ordered mesoporous α-Fe(2)O(3) thin films produced through coassembly strategies using a poly(ethylene-co-butylene)-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent and hydrated ferric nitrate as the molecular precursor. The sol-gel derived α-Fe(2)O(3) materials are highly crystalline after removal of the organic template and the nanoscale porosity can be retained up to annealing temperatures of 600 °C. While this paper focuses on the characterization of these materials using various state-of-the-art techniques, including grazing-incidence small-angle X-ray scattering, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and UV-vis and Raman spectroscopy, the electrochemical properties are also examined and it is demonstrated that mesoporous α-Fe(2)O(3) thin-film electrodes not only exhibit enhanced lithium-ion storage capabilities compared to bulk materials but also show excellent cycling stabilities by suppressing the irreversible phase transformations that are observed in microcrystalline α-Fe(2)O(3).

Ordered mesoporous α-Fe2O3 (hematite) thin-film electrodes for application in high rate rechargeable lithium batteries.

https://iopscience.iop.org/article/10.1088/1468-6996/12/2/025005/pdf

Mesoporous tin-doped indium oxide thin films: effect of mesostructure on electrical conductivity

The 2021 state of technology (SOT) assessment for the indirect liquefaction (IDL) of lignocellulosic biomass to high-octane gasoline (HOG) via methanol and dimethyl ether (DME) intermediates details the techno-economic analysis (TEA) results and technical progress of the pathway since the 2020 SOT report. A detailed process description and collection of underlying assumptions is given the 2015 design report. In 2021, research efforts rigorously quantified the selectivity of DME to aromatic compounds. As a result, the overall carbon selectivity to hydrocarbon products was updated based upon new findings. Additionally, research conducted over the past few years resulted in successful lower temperature regeneration of NREL's Cu/BEA catalyst with favorable implications on catalyst longevity. Discussions with an engineering firm resulted in an update to the excess air requirement for process combustors (including the char combustor, tar reformer combustor, and catalyst regenerator) in which excess air was reduced from 20% excess to 10%. The cumulative effect of the above efforts was used to calculate a minimum fuel selling price for the modeled pathway. Sensitivity cases examining federal carbon tax credits from CO2 capture, product selectivity and yield, catalyst lifetime, and other key financial and process parameters were also considered in this assessment. 

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Alexander Rein

Papers

Ordered mesoporous α-Fe2O3 (hematite) thin-film electrodes for application in high rate rechargeable lithium batteries.

Mesoporous tin-doped indium oxide thin films: effect of mesostructure on electrical conductivity

High-Octane Gasoline from Lignocellulosic Biomass via Syngas and Methanol/Dimethyl Ether Intermediates: 2021 State of Technology