Conversion Mechanism Research Articles

Research on the Influence of Particles and Blade Tip Clearance on the Wear Characteristics of a Submersible Sewage Pump

A submersible sewage pump is designed for conveying solid–liquid two-phase media containing sewage, waste, and fiber components, through its small and compact design and its excellent anti-winding and anti-clogging capabilities. In this paper, the computational fluid dynamics–discrete element method (CFD-DEM) coupling model is used to study the influence of different conveying conditions and particle parameters on the wear of the flow components in a submersible sewage pump. At the same time, the energy balance equation is used to explore the influence mechanism of different tip clearance sizes on the internal flow pattern, wear, and energy conversion mechanism of the pump. This study demonstrates that increasing the particle volume fraction decreases the inlet particle velocity and intensifies wear in critical areas. When enlarging the tip clearance thickness from 0.4 mm to 1.0 mm, the leakage vortex formation at the inlet is enhanced, leading to increased wear rates in terms of the blade and volute. Consequently, the total energy loss and turbulent kinetic energy generation increased by 3.57% and 2.25%, respectively, while the local loss coefficient in regard to the impeller channel cross-section increased significantly. The findings in this study offer essential knowledge for enhancing the performance and ensuring the stable operation of pumps under solid–liquid two-phase flow conditions.

Oscillatory features of German–English sentence processing: Evidence from an EEG study

Aims and objectives: In this study, we investigated the neural oscillatory patterns occurring during sentence-level overt bilingual processing tasks on 46 German–English bilinguals with the intention of finding out if there were task-specific oscillations for this language pair. Methodology: Four tasks, including Language 2 (L2) listening, Language 1 (L1) speaking, L2 shadowing (i.e., repeating a segment of an utterance), and backward interpreting (i.e., orally translating L2 sentences to L1), were implemented with the technique of electroencephalography (EEG). Data and analysis: Data included demographic indices, neural oscillation metrics, and oral production scores from participants. Static spectral analysis, time–frequency analysis, principal components analysis, cross-frequency coupling, and inferential statistics were applied to the data. Findings: The sensory task and articulatory tasks differed greatly in the delta–theta band and the beta–gamma band in terms of time–frequency dynamics. Analyses also revealed variations in a frontal/prefrontal theta component and a distinct gamma component across the four tasks. Moreover, we found a right fronto-temporal theta–gamma coupling unique to backward interpreting. Originality: The task-wise comparison experiment paradigm has rarely been implemented in neuroimaging research on language, especially so in EEG research on bilingualism. Significance: The findings provide novel insights for the understanding of language conversion mechanism and may benefit the training of professional interpreters.

Corrigendum to “A pendulum based frequency-up conversion mechanism for vibrational energy harvesting in low-speed rotary structures”

Corrigendum to “A pendulum based frequency-up conversion mechanism for vibrational energy harvesting in low-speed rotary structures”

Selective lithium recovery from waste lithium-ion batteries by H2SO4 roasting focused on process intensification and conversion mechanism

The purpose of this study is to prove the feasibility, efficiency and selectivity of lithium recovery from waste lithium-ion batteries (LIB) via sulfuric acid roasting-water leaching by thermodynamic analysis and experimental verification. The feasibility was proved by Gibbs free energy calculations and experiments. Then, the effects of H2SO4 concentration, roasting temperature and roasting time were assessed on the leaching rate of valuable metals. The results indicate that the leaching efficiency of lithium increases firstly and then decreases with the increase of H2SO4 concentration, roasting temperature and roasting time, more than 91 % lithium are leached under optimized experimental conditions: 50 wt% H2SO4, roasting temperature of 650°C, and roasting time of 2 h. Meanwhile, the selectivity of lithium is up to 88 % which means overwhelming majority lithium have been separated completely. In addition, the factors which cause sintering phenomenon such as high temperature and longtime roasting will change the microstructure of roasted product extremely, which is inconducive to the subsequent water leaching. The investigations of the phase conversion mechanism by thermodynamic simulation and instrumental characterization indicated that the leaching behaviors of valuable metals might be influenced by the different reaction pathways of the compounds while changing roasting conditions. The recovery process can be divided into two stages: the partial structure of LiNixCoyMnzO2 was destroyed to form metal sulfates at ambient temperature and the solid phase reaction between unreacted LiNixCoyMnzO2 which contained Li+ in the unstable layered structure with transition metal sulfates at high temperature. The fully reduced low-valence states are mainly (NiO)0.75(MnO)0.25 and CoO, and basically all Li within the crystalline LiNixCoyMnzO2 was de-intercalated and transformed to soluble Li2SO4. These results further confirm the advantages of H2SO4 roasting on selective Li recovery, and provide a better understanding of conversion mechanism by combining theory and experiments.

Unraveling the Spin-to-Charge Current Conversion Mechanism and Charge Transfer Dynamics at the Interface of Graphene/WS2 Heterostructures at Room Temperature.

We report experimental investigations of spin-to-charge current conversion and charge transfer (CT) dynamics at the interface of the graphene/WS2 van der Waals heterostructure. Pure spin current was produced by the spin precession in the microwave-driven ferromagnetic resonance of a permalloy film (Py=Ni81Fe19) and injected into the graphene/WS2 heterostructure through a spin pumping process. The observed spin-to-charge current conversion in the heterostructure is attributed to the inverse Rashba-Edelstein effect (IREE) at the graphene/WS2 interface. Interfacial CT dynamics in this heterostructure was investigated based on the framework of the core-hole clock (CHC) approach. The results obtained from spin pumping and CHC studies show that the spin-to-charge current conversion and charge transfer processes are more efficient in the graphene/WS2 heterostructure compared to isolated WS2 and graphene films. The results show that the presence of WS2 flakes improves the current conversion efficiency. These experimental results are corroborated by density functional theory (DFT) calculations, which reveal (i) Rashba spin-orbit splitting of graphene orbitals and (ii) electronic coupling between graphene and WS2 orbitals. This study provides valuable insights for optimizing the design and performance of spintronic devices.

Conversion mechanisms and transformed waves for the (3 + 1)-dimensional nonlinear equation

In this paper, we focus on investigating the (3 + 1)-dimensional nonlinear equation which is used to describe the propagation of waves in the shallow water. The study begins with the application of the Hirota bilinear method to obtain N-soliton solution. Building on this foundation, the research delves into the construction of first-order breather wave by imposing complex conjugate constraints on the parameters of two solitons. Further analysis of the characteristic lines of breathers leads to the derivation of conversion conditions. Under this specific condition, a series of nonlinear transformed waves are presented, including quasi-kink solitons, W-shaped kink solitons, oscillation W-shaped kink solitons, multipeaks solitons, quasi-periodic waves, and line rogue waves. Each of these transformed waves exhibits unique structural and dynamic properties, enriching the understanding of wave behavior in higher-dimensional nonlinear systems. The study also explores the nonlinear superposition mechanism between solitary wave and periodic wave. This mechanism elucidates the formation process of nonlinear waves, explaining how their locality and oscillatory characteristics emerge from the superposition of different wave components. Moreover, the geometric properties of the two characteristic lines of the waves are analyzed to understand the time-varying nature of the transformed waves. This temporal analysis is crucial for predicting the evolution and interaction of these waves over time. Finally, the research extends to the higher-order breather wave and explores the interactions among various waves. These interactions reveal the complex dynamics that may arise in the (3 + 1)-dimensional nonlinear systems and provide deeper insights into the interactions among different wave structures.

Investigation of the mechanism and interaction of nitrogen conversion during lignin/glutamic acid co-pyrolysis

Biomass pyrolysis has the potential to be transformed into valuable chemicals and fuels. Nitrogenous chemicals exert a substantial influence on the quality of bio-oil. Studying the impact of lignin on the transformation of nitrogen-containing elements in biomass during biomass pyrolysis is crucial for achieving efficient and effective utilization of biomass resources. In this study, tube furnace experiments, thermogravimetric infrared experiments (TG-FTIR), and gas chromatography-mass spectrometry (Py-GC/MS) were used to investigate the interactions of typical lignins (vanillin and syringol), nitrogenous components (glutamic acid), and the effect of lignin on the pyrolysis gas release of glutamic acid and the pyrolysis products during the co-pyrolysis process. In addition, the impact of lignin on the effect of pyrrolidone formation from glutamic acid was investigated in this study in conjunction with quantum chemical calculations. The experimental findings demonstrated that the co-pyrolysis of lignin and glutamic acid resulted in a reduction in the pyrolysis temperature. This reduction facilitated the release of HCN, NH3, and CO2 while notably impeding the formation of nitrogen-containing compounds in the oil. The nitrogen concentration in the pyrolysis oil declined from 97 % to a range of 51.06–79.63 %, and the inhibitory impact decreased as the pyrolysis temperature increased. At an elevated pyrolysis temperature of 800 °C, lignin facilitated the decarboxylation process of glutamic acid, resulting in an increased production of pyrrolidone.Simulation results demonstrated that the lowest energy barrier paths were the dehydration condensation process and the Maillard reaction involving glutamic acid and lignin and their pyrolysis intermediates, with a particular competitive connection between the two pathways. The results explained the interaction mechanism between the two pyrolysis products and provided a fundamental theoretical basis for nitrogen conversion in biomass pyrolysis.

Vector angular spectrum model for light traveling in scattering media

Strongly scattering media disrupt both the wavefront distribution and the polarization state of the incident light field. Controlling and effectively utilizing depolarization effects are crucial for optical applications in highly scattering environments, such as imaging through dense fog. However, current simulation models have difficulty simulating the evolution of vector light fields within scattering media, posing challenges for studying vector light fields in strongly scattering environments. Here, we propose the Vector Angular Spectrum (VAS) model for simulating the propagation of vector light fields within scattering media. By introducing the angular spectrum distribution of vector light scattering and polarization conversion mechanisms, this model can simulate the depolarization effects of vector light propagating through strongly scattering media. The VAS model has also been used to investigate the focusing of vector scattered light through scattering media. Furthermore, the simulation results of the model have been validated through experiments. The proposed VAS model is expected to play a role in the theoretical research of vector scattered light and optical applications in strongly scattering environments.

Synergistic engineering of heteroatomic N-doping and PPy modification in flower-like vanadium sulfide anode enables stable sodium storage

Vanadium sulfide, an appealing anode candidate for sodium ion batteries (SIBs), still encounters considerable volume fluctuation and sluggish Na+ diffusion kinetics, which inevitably gives rise to unsatisfactory rate capability and severe capacity decay. Herein, we successfully designed and constructed an outstanding sodium-storage feature and exceedingly stable anode for SIBs in the form of three-dimensional flower-like architecture composing of phosphorus doped VS2 wrapped by conductive elastic polypyrrole (PPy) layer (i.e., P-VS2@PPy). Through leveraging the multifunctional synergistic effect of composition and structure, involving enhanced electronic conductivity, reduced volumetric fluctuation, accelerated charge/ion transfer efficiency, and remarkable surface-capacitive behaviors can guarantee significantly enhanced electrochemical sodium-storage ability of P-VS2@PPy composites. As a consequence,such P-VS2@PPy is endowed with desirable rate characteristic accompanied with long-period cyclic lifespan (436.7 mAh/g at 20.0 A/g after 2600 cycles), which far outperform contrastive P-VS2 and pure VS2 samples. Meticulous kinetic analysis combined with theoretical simulations conclude that phosphorus doping and PPy coating have substantial effects on strengthening ionic and electron diffusion kinetics. Thorough examination and analysis of the insertion and conversion mechanisms of P-VS2@PPy was conducted through ex situ tests, revealing superior reversible phase transformation between original VS2, intermediate NaVS2, and final Na2S/V. Additionally, a practical application test demonstrates that sodium ion full-cell and hybrid capacitor based on P-VS2@PPy anode showcase significant capacity contribution and outstanding specific energy output, capable of effortlessly lighting up a LED screen.

Sulfur atom occupying surface oxygen vacancy to boost the charge transfer and stability for aqueous Bi2O3 electrode

Oxygen vacancies (Ov) within metal oxide electrodes can enhance mass/charge transfer dynamics in energy storage systems. However, construction of surface Ov often leads to instability in electrode structure and irreversible electrochemical reactions, posing a significant challenge. To overcome these challenges, atomic heterostructures are employed to address the structural instability and enhance the mass/charge transfer dynamics associated with phase conversion mechanism in aqueous electrodes. Herein, we introduce an atomic S–Bi2O3 heterostructure (sulfur (S) anchoring on the surface Ov of Bi2O3). The integration of S within Bi2O3 lattice matrix triggers a charge imbalance at the heterointerfaces, ultimately resulting in the creation of a built-in electric field (BEF). Thus, the BEF attracts OH− ions to be adsorbed onto Bi within the regions of high electron cloud overlap in S–Bi2O3, facilitating highly efficient charge transfer. Furthermore, the anchored S plays a pivotal role in preserving structural integrity, thus effectively stabilizing the phase conversion reaction of Bi2O3. As a result, the S–Bi2O3 electrode achieves 72.3 mAh g−1 at 10 A g−1 as well as high-capacity retention of 81.9% after 1600 cycles. Our innovative S–Bi2O3 design presents a groundbreaking approach for fabricating electrodes that exhibit efficient and stable mass and charge transfer capabilities. Furthermore, it enhances our understanding of the underlying reaction mechanism within energy storage electrodes.

Energy coupling and surge wave superposition of upstream series double surge tanks of pumped storage power station

Pumped storage power station with surge tank is common, and surge wave superposition can cause more dangerous water levels. This paper aims to study the energy coupling and surge wave superposition of upstream series double surge tanks of pumped storage power station. Firstly, the simulation model of pumped storage power station based on method of characteristics is established. Combined operating conditions are illuminated. Then, surge wave control strategies coupling gravitational search algorithm, relative objective proximity and marginal analysis principle are designed. Coupling control domains are determined to perform surge wave superposition analyses under single objective and multi-objective. Finally, the energy coupling and conversion mechanisms are revealed. The results show that the coupling control domains of combined operating conditions with same initial operating condition are the same. Control domains for undamped and damped systems contain two and three sub control domains, respectively. Based on energy conversion mechanisms between discharges and water levels, the number of discharge superposition points of pipelines affects energy coupling strength by changing coupling oscillations of water levels in surge tanks, which is related to the pipeline parameters, surge tank parameters and system damping. Energy coupling affects surge wave superposition by changing the actual control water level.

Mechanochemical removal and recovery of fluorine from hazardous fluorine-containing solid waste: Experiments and mechanisms

Large amounts of hazardous fluorine-containing solid waste (HFSW) are produced globally each year. Recycling HFSW not only conserves valuable F resources but also serves as a crucial step towards environmental sustainability. This work proposed an efficient and green approach for F removal and recovery from the HFSW using a mechanochemical method. The results showed that MgF2 component in the HFSW can be almost completely converted to NaF and Mg(OH)2 by the mechanochemical force with NaOH as co-grinding agent. A possible NaOH mechanochemical decomposition and conversion mechanism of MgF2 is also proposed based on thermodynamics, XRD, TEM and DFT calculations. By optimizing the mechanochemical conditions, such as NaOH concentration of 35 mol/L, ball-to-material ratio of 10:1 g/g, liquid-solid-ratio of 1.8 mL/g, mechanical activation speed of 600 rpm, and mechanical activation time of 150 min, 99.51 % of F in the HFSW can be leached. Finally, 98.69 % purity of NaF product was recovered from the as-obtained F-containing leachate through N235 extraction and evaporative crystallization. The results of this work are expected to provide a promising solution for F removal and recovery from HFSW.

Flexible Thermoelectric and Piezoelectric Hybrid Energy harvester by Adopting a Multifunctional Cellulose-based Composite Film

Thermoelectric (TE) and piezoelectric (PE) energy harvesting are the most advantageous conversion mechanisms for converting energy generated by the human body into electrical energy, respectively. However, the development of a hybrid energy harvester is essential for achieving high energy conversion efficiency since a single energy harvester cannot convert enough energy. Herein, we present a flexible TE-PE hybrid energy harvester (f-TPHEH) based on a self-assembled single film consisting of Bi2Te2.7Sn0.3 particles, BaTiO3 nanoparticles, and cellulose. The fabricated f-TPHEH exhibited a maximum TE output power of 18.47 nW and a PE instantaneous output of 13.5 nW under integrated thermal and bending conditions (ΔT = 40 K, bending displacement = 7 mm). We conducted a theoretical analysis using multiphysics simulation based on finite element analysis to support the experimental measurements of the fabricated f-TPHEH. In addition, to demonstrate the mechanical stability of the cellulose matrix-based f-TPHEH, a durability test was performed up to 5,000 cycles of bending deformation. This study presents a method for developing the flexible hybrid energy harvester using a low-cost and simple fabrication process.

Characterisation of Pseudomonas mosselii H6 for aerobic denitrification: stoichiometry and reaction kinetics

The application of aerobic denitrifying bacteria in biological nitrogen removal has been of great interest. However, the mechanism of nitrogen conversion by aerobic denitrifying bacteria is unclear due to the lack of stoichiometry and kinetic studies. Therefore, this study aimed to investigate the stoichiometry and kinetics of aerobic denitrification using Pseudomonas mosselii H6 as a model strain. The results showed that the stoichiometric equations of strain H6 under different nitrogen source conditions were obtained by nitrogen balance analysis; the concentrations of different limiting substrates were set and combined with the multi-substrate Monod kinetic equation to fit the half-saturation constants of COD, ammonia, nitrate and nitrite nitrogen for strain H6, which were 230.1008, 25.3435, 4.1009 and 23.4601 mg/L, respectively; based on the model of “two-step denitrification”, the numerical simulation of the growth and aerobic denitrification of strain H6 under different limiting substrate concentrations was carried out by using AQUASIM software to test the validity of stoichiometric coefficients and kinetic constants and perfect fitting results were obtained. These parameters will help to simulate the growth and denitrification performance of aerobic denitrifying bacteria and provide an experimental basis for further quantitatively elucidating the mechanism of action in the aerobic denitrification process.

AI-enhanced backpack with double frequency-up conversion vibration energy converter for motion recognition and extended battery life

With growing interest in physical activities, wearable device sales have been increasing each year due to their help in tracking movement. However, keeping these devices running for a long time is still a key challenge. This paper presents an AI-enhanced backpack equipped with a hybrid vibration energy converter that integrates piezoelectric (PE) and electromagnetic (EM) technologies, featuring a double frequency-up conversion (FUC) mechanism. The PE unit enables efficient motion recognition, while the EM unit extends battery life via kinetic energy harvesting. The double FUC mechanism boosts human motion signal strength and resolution by converting sub-Hertz frequencies to hundreds of Hertz. This makes the device particularly effective in environments with performance constraints and interference. By adopting deep learning techniques, the system maintains a high motion recognition accuracy of 97.33 % even under low data sampling rates and significant noise interference. The EM unit effectively harvests kinetic energy, generating an average output power of 4.5 mW during activities such as running at 4.5 Hz, despite of the device’s compact size. Additionally, a power management circuit with human motion-stimulated switch optimizes battery life by managing the system’s sleep and active states. This innovative energy management approach ensures that during human activity, the system conserves energy by remaining in sleep state for at least 30 % of the time, significantly extending battery life and enhancing the backpack’s suitability for outdoor applications.

Bioelectricity drives transformation of nitrogen and perfluorooctanoic acid in constructed wetlands: Performances and mechanisms

In this study, constructed wetland-microbial fuel cell (CW-MFC) filled with modified basalt fiber (MBF) via iron modification was utilized for treating perfluorooctanoic acid (PFOA) containing sewage. Results showed the significant promotion by bioelectricity on ammonium and total nitrogen by 7.80–8.14 %. Although such enhancement was suppressed by PFOA, higher removal was still observed with closed circuit, and PFOA removal also increased by 9.05 %. Bioelectricity contributed to enrichment of bacteria involved in nitrifying (Nitrospira and Ellin6067), denitrifying (like Thauera and Dechloromonas), iron redox (Geobacter), and sulfate-reducing (Desulfobacter), aligned with up-regulated of functional genes, including amoA, narG , napA, narK, narS, nrfA, sulp and sqr. Enrichment of autohydrogenotrophic and sulfide-oxidizing autotrophic denitrifiers, and nitrate dependent iron oxidation bacteria by bioelectricity all promoted denitrification. Moreover, bioelectricity boosted relative abundance of organic compounds degradation enzymes, such as dehydrogenase, decarboxylase, and dehalogenase, supporting the enhancement on PFOA removal. Generally, PFOA was converted to short-chain perfluorocarboxylic acids (PFCAs) via decarboxylation, hydroxylation, HF elimination, hydrolysis, F- elimination, C-C bond scission, and dehydration in CW-MFC. The final PFCAs-products determined was perfluorobutyric acid. This work estimated feasibility of treating PFOA containing sewage by CM-MFC, and offered new insights on enhancing mechanisms of nitrogen and PFOA conversion.

Photoconvertible and Photoactivatable Perylene BisImide Based on Photocyclization

AbstractPhotomodulable fluorophores constitute advanced materials as they possess the ability to modify their photophysical properties upon photoirradiation. A new mechanism of photoconversion is recently established, called Directed Photooxidation Induced Conversion based on the coupling of fluorophores with Aromatic Singlet oxygen Reactive Moieties (ASORMs). In this work, The Directed Photooxidation Induced Conversion (DPIC) mechanism is intended to be applied to Perylene BisImide (PBI) due to its appealing photophysical properties. The experimental results showed that coupling two ASORMs to the PBI core, here furan and pyrrole, led to impressive photomodulable fluorophores. While PBI‐F exhibited a photoconversion of 100 nm shift, PBI‐P displayed an 80‐fold fluorescence intensity enhancement upon photoactivation. Analysis of the photoproducts showed that the conversion do not involve an addition of singlet oxygen on the ASORM. Instead, photoconversion occurred through efficient successive photocyclizations. Finally, intracellular vesicles are successfully photoconverted by means of endocytosed PLGA‐polymer nanoparticles loaded with PBI‐F. This study highlights the unique capability of furan‐ and pyrrole‐conjugated fluorophores to enable advanced optical materials with phototransformation properties.

Advances in Phosphogypsum Calcination and Decomposition Processes in Circulating Fluidized Beds.

Phosphogypsum (PG) is an industrial hazardous waste product discharged during wet-process phosphoric acid production. Once crystallized, the byproduct PG is filtered and separated from the liquid-phase product and sluiced to the disposal area near the production site for storage, seriously threatening the harmonious symbiosis between humans and nature. Therefore, devising effective solid waste management and cleaner production programs to contain and eliminate PG is of interest to researchers. In this study, the utilization status of PG is comprehensively reviewed, and a feasibility pathway for resourceful recovery of PG is proposed. The key challenges and countermeasures for the high-temperature calcination and decomposition of PG are analyzed and discussed. The visualization analysis based on bibliometrics reveals that the maximum recovery of abundant calcium (as CaO) and sulfur (as SO2) in PG and their utilization for the copreparation of calcium-based materials and sulfuric acid are the most suitable solutions for the large-scale application of PG. Five challenges that restrict the commercial promotion of PG calcination and decomposition processes are perfecting the calcium-sulfur conversion mechanism, establishing a process strengthening strategy, developing value-added technology routes, mastering unit scale-up regularity, and conducting sustainable performance assessment. Industrial applications are expected within 10-15 years.

Programming Hydrogen Bonds for Reversible Elastic‐Plastic Phase Transition in a Conductive Stretchable Hydrogel Actuator with Rapid Ultra‐High‐Density Energy Conversion and Multiple Sensory Properties

AbstractSmart hydrogels have recently garnered significant attention in the fields of actuators, human‐machine interaction, and soft robotics. However, when constructing large‐scale actuated systems, they usually exhibit limited actuation forces (≈2 kPa) and actuation speeds. Drawing inspiration from hairspring energy conversion mechanism, an elasticity‐plasticity‐controllable composite hydrogel (PCTA) with robust contraction capabilities is developed. By precisely manipulating intermolecular and intramolecular hydrogen‐bonding interactions, the material's elasticity and plasticity can be programmed to facilitate efficient energy storage and release. The proposed mechanism enables rapid generation of high contraction forces (900 kPa) at ultra‐high working densities (0.96 MJ m−3). Molecular dynamics simulations reveal that modifications in the number and nature of hydrogen bonds lead to a distinct elastic‐plastic transition in hydrogels. Furthermore, the conductive PCTA hydrogel exhibits multimodal sensing capabilities including stretchable strain sensing with a wide sensing range (1–200%), fast response time (180 ms), and excellent linearity of the output signal. Moreover, it demonstrates exceptional temperature and humidity sensing capabilities with high detection accuracy. The strong actuation power and real‐time sensory feedback from the composite hydrogels are expected to inspire novel flexible driving materials and intelligent sensing systems.

How Cryo-EM Revolutionized the Field of Bioenergetics

Abstract Ten years ago, the term “resolution revolution” was used for the first time to describe how cryogenic electron microscopy (cryo-EM) marked the beginning of a new era in the field of structural biology, enabling the investigation of previously unsolvable protein targets. The success of cryo-EM was recognized with the 2017 Chemistry Nobel Prize and has become a widely used method for the structural characterization of biological macromolecules, quickly catching up to x-ray crystallography. Bioenergetics is the division of biochemistry that studies the mechanisms of energy conversion in living organisms, strongly focused on the molecular machines (enzymes) that carry out these processes in cells. As bioenergetic enzymes can be arranged in complexes characterized by conformational heterogeneity/flexibility, they represent challenging targets for structural investigation by crystallography. Over the last decade, cryo-EM has therefore become a powerful tool to investigate the structure and function of bioenergetic complexes; here, we provide an overview of the main achievements enabled by the technique. We first summarize the features of cryo-EM and compare them to x-ray crystallography, and then, we present the exciting discoveries brought about by cryo-EM, particularly but not exclusively focusing on the oxidative phosphorylation system, which is a crucial energy-converting mechanism in humans.