Amgad R. Rezk

The chemical industry is the largest industrial energy consumer and the third-largest emitter of CO2 globally. Despite efforts to enhance energy efficiency, many chemical reactions still require significant external energy due to fundamental thermodynamic barriers. Thus, transitioning to a sustainable chemical industry requires new renewable energy or catalytic technologies that reduce energy demand. In catalytic systems, flowing liquids, moving parts, and gas separation mean local static charge is often generated on the nanoscale. This review explores the static charge formation at solid–solid, solid–liquid, and solid–gas interfaces, such as those that occur in catalytic reactions, and then extends this discussion to a deeper focus on how these generated static charges can be used for catalysis, including electrostatic catalysis, static charge electrochemistry, and contact electrocatalysis (CEC). CEC, where motion-induced charge separation leads to local static charge formation, is then specifically examined, exploring why and how it has emerged as an exciting tool to enable these green chemical transformations. The focus is to highlight the most recent developments in CEC, with mechanistic interpretation, factors that affect CEC performance, and emerging applications, and to provide outlook and guidance for the field─specifically highlighting the need to build structure–property relationships for CEC performance and static charge formation for target chemical reactions.

Characterizing metal solubilities in post-transition-based liquid metals remains challenging due to their inherent opacity to conventional light-based analytical techniques. In this work, we present an in situ heating methodology within a transmission electron microscope that enables direct probing of the behavior of solid metal solutes within the local boundaries of liquid metal nanodroplets. Specifically, we show that the solubility of transition and precious metals in liquid state metallic solvents is dependent on the droplet size that contains them due to the internal Laplace pressure. We also show that the dissolution behaviors of solute metals in gallium–indium and gallium–indium–tin eutectic nanodroplets deviate from that of pure gallium, with solvent composition influencing solubility. Moreover, entropy-driven solubility effects are studied in multicomponent alloys that contain several solutes. The outcomes of this work are crucial for advancing liquid metal-based functionalities of soft systems, particularly for catalysis.

Triboelectric nanogenerators (TENGs) are a key emerging technology for powering wearable, implantable, remote, and autonomous small-scale electronics. Despite extensive reports, there is often a lack of rigor in reporting the mechanical testing conditions used to measure electrical performance in TENGs. Herein, we systematically vary the separation speed in contact–separation TENGs between 12.5 and 700 mm s–1 (both experimentally and via simulations) and measure a corresponding increase in power density from 10–7 to 10–4 W (along with analogous increases in measured current and voltage)-without changing any other material property or parameter. The transferred charge density (on the external electrodes, as separate from the surface charge density) also increased from 0.3 to 10 nC cm–2, demonstrating (along with supporting computational simulation experiments) that large changes in measured output can arise from testing conditions rather than changes in material chemistry or device structure. These results demonstrate the importance of separation speed in contextualizing literature reports of TENG performance and highlight the need to dramatically improve data reporting for the field. To address this, we propose the need to report a standard and consistent set of testing parameters for contact separation. Adoption of these conditions will enable meaningful benchmarking of TENGs and allow the field to progress more effectively.

Covalent organic frameworks (COFs) are promising materials for wide-ranging applications. Challenges with coating them onto surfaces have however limited their wider implementation in practice. We report an acoustomicrofluidic nebulization platform that enables rapid, one-step synthesis of highly crystalline COFs and their direct deposition as a coating under ambient conditions. Demonstrated with both two- and three-dimensional imine-based COFs, the method yields uniform COF films with nanometer to micrometer thicknesses, tuned simply by adjusting the nebulization time. Unlike conventional COF coating approaches, this strategy eliminates the need for any postsynthetic substrate heating or processing, thereby offering a general and scalable route for fabricating functional COF coatings on a variety of sensitive and complex substrates, including living tissue. As proof of concept, we demonstrate that COFs can constitute protective coatings on plant leaves for solar ultraviolet shielding, thus highlighting the potential of the platform to extend the deployment of COFs in real-world devices, biological systems, and environmental interfaces.

Engineering the physical properties of metal-organic frameworks (MOFs) to improve their performance has been a key focus area for establishing their use in a variety of applications. While some synthesis strategies have shown promise in this regard, a method that can simultaneously give rise to unique properties in the MOF structure across multiple dimensions (e.g., the nano-, meso-, and macro-scales), which can be critical for a number of practical applications, has never been reported. Herein, we report an acoustomicrofluidic platform that concurrently facilitates such multiscale manipulation of the MOFs' physical properties. In just several minutes at room temperature, large (O(10-100 μm)) monolithic superstructures of UiO-66 MOFs (a MOF model with excellent stability) can be synthesized with highly desirable properties. These properties include hierarchical (micro- and meso-scale) porosity and nanoscale framework-level defects, all of which are absent in conventional-prepared UiO-66 with solvothermal synthesis. We show (as examples of the benefits of simultaneously enhancing the MOF properties on multiple dimensional levels) their practical application for simultaneous capture and degradation of large dye molecules, and for UV photodetection with superior responsivity.

Materials and devices that harvest acoustic energy can enable autonomous powering of microdevices and wireless sensors. However, traditional acoustic energy harvesters rely on brittle piezoceramics, which have restricted their use in wearable electronic devices. To address these limitations, this study involves the fabrication of acoustic harvesters using electrospinning of the piezoelectric polymer PVDF-TrFE onto fabric-based electrodes. Two-dimensional (2D) Ti₃C₂T_x MXene flakes were used to induce polarization locking of the electrospun PVDF-TrFE for optimal electromechanical performance of PVDF-TrFE. The mechanically robust, lightweight, and flexible device was demonstrated to detect and harvest energy in the sound frequency range of 50 to 1000 Hz at sound levels between 60 and 95 dB, while exhibiting a high sensitivity of 37 VPa^-1, which is higher than previously reported values for PVDF-based sound harvesters. The maximum output power can reach 19 mW/cm³ under 200 Hz and 95 dB. The development of this material opens a future pathway for powering small electronic devices, such as implantable biomedical devices, smart wearable technology, and remote Internet-of-Things devices.

An unconventional yet facile low-energy method for uniquely synthesizing neat poly(vinylidene fluoride) (PVDF) films for energy harvesting applications by utilizing nanoelectromechanical vibration through a ‘piezo-to-piezo’ (P2P) mechanism is reported. In this concept, the nanoelectromechanical energy from a piezoelectric substrate is directly coupled into another polarizable material (i.e., PVDF) during its crystallization to produce an optically transparent micron-thick film that not only exhibits strong piezoelectricity, but is also freestanding—properties ideal for its use for energy harvesting, but which are difficult to achieve through conventional synthesis routes. We show, particularly through in situ characterization, that the unprecedented acceleration associated with the nanoelectromechanical vibration in the form of surface reflected bulk waves (SRBWs) facilitates preferentially-oriented nucleation of the ferroelectric PVDF β-phase, while simultaneously aligning its dipoles to pole the material through the SRBW's intense native evanescent electric field . The resultant neat (additive-free) homopolymer film synthesized through this low voltage method, which requires only —orders-of-magnitude lower than energy-intensive conventional poling methods utilizing high kV electric potentials, is shown to possess a 76% higher macroscale piezoelectric charge coefficient d₃₃, together with a similar improvement in its power generation output, when compared to gold-standard commercially-poled PVDF films of similar thicknesses.

The world is facing grand challenges in energy security, environmental pollution, and sustainable use (and re‐use) of resources. Electrochemical processes, incorporating electrosynthesis, electrochemical catalysis, and electrochemical energy storage devices, provide pathways to address these challenges via green chemistry. However, the applicability of electrochemical processes for these systems is limited by the required energy input, the “electrons” in electrochemistry. Electrocatalysis as a subset of electrochemistry is set to underpin many of the United Nations Sustainable Development Goals, including “Affordable and Clean Energy” through the production of future fuels and abatement of carbon emissions; “Responsible Consumption and Production” through recycling and degradation of waste; and “Climate Action” through CO₂ (and other greenhouse gas) remediation. The rise of green photovoltaic power has lowered the carbon cost of these electrons, making electrocatalysis an even more viable, green(er), chemical conversion pathway. This perspective highlights the need for comprehensive understanding of catalyst structure via in situ and operando analysis to complement device design considerations. The challenges faced by the field of electrocatalysis in data reporting, elimination of electrochemical artifacts, catalyst stability, and scaling to industrial relevance, along with opportunities, emerging tools, are discussed with a view to achieve the maximum ‘potential’ of electrocatalysis.