Pumping Experiments Research Articles

CO2 Hydrogenation through Electrochemical Hydrogen Activation in a Gas-Vapor Fed Reactor

An attractive concept in the chemical manufacturing industry is the adoption of a circular carbon economy, which can include continuous capture and conversion of CO2 into industrially relevant chemical feedstocks. This has driven considerable research interest in electrochemical CO2 reduction.1 Despite this popularity, major challenges remain even for the most advanced CO2 reduction reactors, including low conversion rates and energy efficiencies; moreover, in many cases, multiple carbon-containing products are generated, which add to costs for downstream separation.2 By contrast, thermochemical CO2 hydrogenation is well established and typically demonstrates higher energy efficiency and selectivity compared to electrochemical CO2 reduction.3,4 This notable contrast drives our interest in better understanding the physics that governs differences in reactivity between thermocatalytic and electrocatalytic CO2 reduction reactors. To address these questions, we are pursuing a unique approach that involves feeding humidified CO2 and H2, respectively, to the cathode and anode of an electrochemical membrane-electrode assembly (MEA). This presentation will cover initial work we have undertaken to design and validate this reactor for the study CO2 electro-reduction.The overall design of our reactor resembles a hydrogen fuel cell fed with humidified H2 and CO2. Thus, it was initially benchmarked through operation as an electrochemical hydrogen pump, wherein humidified Ar was fed to the cathode and humidified H2 was fed to the anode with Pt/C as the catalyst on each side of the membrane. Under these conditions, a cation exchange membrane (CEM) readily generated current densities in excess of 1 A/cm2 with monotonic decreases in polarization with increased temperature at fixed current. We then undertook analogous hydrogen pumping experiments using anion exchange membranes (AEM) that had been ion-exchanged with hydroxide, carbonate, and bicarbonate anions. We observed net proton transport between the anode and cathode chambers in each case, albeit with higher ionic resistance for AEMs in the bicarbonate form.We then undertook further studies to demonstrate the ability to reduce CO2 using H2 fed to the anode. This operating mode eliminates the need for a liquid anode feed, which dramatically reduces the driving force for CO2 crossover via bicarbonate formation. Moreover, the Pt/C anode catalyst is expected to oxidize hydrogen with minimal polarization, allowing the total cell polarization to be interpreted simply as the cathode potential on the RHE scale. CO2 reduction experiments were carried out using commercial Cu/C catalyst with online gas chromatography and NMR for product analysis of volatile and condensable products, respectively. Operation with a CEM yielded only H2(g) at the cathode, but initial experiments with an AEM in the carbonate/bicarbonate form gave high selectivity to ethanol at 70 oC.

Evaluating the productivity of basement rock aquifers for sustainable groundwater development in sub-Sahara Africa using borehole pumping experiments and geophysical data

Ensuring all-year-round groundwater availability in the basement complex regions of sub-Sahara Africa requires careful combinations of strategies for exploration, development, and management of groundwater resources. The productivity of the basement aquifer of sub-Sahara Africa, SSA, was evaluated in terms of the volume of water produced per unit time, the aquifer transmissivity, hydraulic conductivity, specific capacity, and the thickness of the water-bearing zones using a suit of data from borehole pumping experiments, geophysical surveys, and lithologic logs from Opaque Field in sub-Sahara Africa. Findings from the study have been used to classify the basement complex aquifers of sub-Sahara Africa into three categories: marginally productive, low productive, and moderately productive. Weathered and fractured zones were found to be bright spots for groundwater storage, and aquifer productivity correlates with topography and the thickness of the weather zones. Most of the boreholes located on the low topographic heights were found to have the highest groundwater discharge, transmissivity, and hydraulic conductivity. Further, the study showed that the popular models used for estimating aquifer properties are unsuitable for basement complex aquifers. The results of the models are exaggerated when compared to the pumping test results. Cases of dry holes or poorly performing wells in the basement complex terrain may be attributed to the exaggeration. Consequently, two new and novel quantitative models were proposed and tested for evaluating the productivity parameters of basement aquifers of SSA for optimal selection of sites for groundwater development. The aquifer productivity maps computed with the new quantitative models show striking similarities to those computed from the pumping tests results and confirmed the appropriateness of the new quantitative models. The appropriate pumping device, pump operation time, and installation depth were recommended for the boreholes producing groundwater from the three categories of aquifers identified in this study.

A novel interpretable semi-supervised graph learning model for intelligent fault diagnosis of hydraulic pumps

Although deep learning has gained popularity in the field of fault diagnosis, its limitations are also equally apparent, including: (1) heavy reliance on a substantial volume of labeled samples; (2) a lack of interpretability. To confront these issues, this article proposes a novel interpretable semi-supervised graph learning model for intelligent fault diagnosis of hydraulic pumps. A comparison between the raw data and the model's hidden layer representations is conducted to minimize feature loss. The model commences by preliminarily learning fault information that is intermixed with noise, leveraging a substantial corpus of unlabeled data. In response to the intricacy of downstream tasks, an interpretable feature reconstruction module is introduced. This module employs a nonlinear surrogate model to fit and elucidate the learned features, embedding the explanation scores into the features to reconstruct the samples, a process utilized for model fine-tuning. The feature reconstruction module capitalizes on the explanatory power of the surrogate model, guiding the model to concentrate more on features with significant impact. This method not only provides interpretability during model training but also expedites the convergence speed of the model. Finally, two hydraulic pump experiment cases are used to verify the effectiveness of the model, and the results show that our method has obvious advantages in reducing label dependence and increasing model reliability for decision making.

Enhancing the sensitivity of spin-exchange relaxation-free magnetometers using phase-modulated pump light with external Gaussian noise.

An optical pumping scheme is proposed for reducing the gradient of electron spin polarization and suppressing light source noise in a spin-exchange relaxation-free magnetometer. This is achieved by modulating only the phase of a narrow-linewidth pump light field with external Gaussian noise. Compared to the absence of phase modulation, the uniformity of electron spin polarization was improved by over 40%, and the light-frequency noise suppression ratio of the magnetometer was enhanced by 4.3 times. Additionally, the response of the magnetometer was increased by 54%, resulting in a sensitivity of 0.34 fT/Hz1/2 at 30 Hz. The applicability of this scheme can extend to other optical pumping experiments involving large atom ensembles requiring uniform electron spin polarization distribution, which is beneficial for developing ultra-high sensitivity and high stability magnetometers essential for magneto-cardiography and magneto-encephalography research applications.

Ecological and geological security risk assessment of underground space development in cold and arid canyon cities-Taking Ping'an District, Haidong City, Qinghai Province, as an example.

The ecological and geological problems caused by the rise of groundwater level due to the development of underground space in cold and arid canyon cities are particularly typical. Reasonably assessing the ecological and geological security risks of utilizing underground space is conducive to reducing the occurrence of ecological and geological problems during the construction and operation of underground engineering projects. Taking Ping'an District of Haidong City as an example, the topography and geomorphology of the research area were investigated in the field, and the distribution of topography and geomorphology in the research area was understood; through geological drilling and geotechnical engineering testing, the distribution of different strata in the research area was obtained; through pumping and seepage experiments, the recharge, runoff, and discharge relationship between surface water and groundwater in the research area and the water abundance of different strata are obtained, and the causes and mechanisms of geological safety risks in forest and grassland ecosystems, farmland ecosystems, and human settlements ecosystems were analyzed based on literature. Corresponding ecological geological safety risk assessment index systems and methods were established, and the ecological geological safety risks before and after the development of underground rail transit projects along both banks of the Huangshui River in the study area were evaluated. PRACTITIONER POINTS: The development of underground space in canyon type cities can easily lead to ecological and geological problems. Taking Haidong City, Qinghai Province, as an example, this study investigates the causes of ecological and geological problems caused by the development of underground spaces in canyon type cities. An ecological geological security risk assessment index system and method for canyon-type cities were established. An evaluation was conducted on the ecological and geological safety risks before and after the development of the underground rail transit projects on both sides of the research area.

Development of Dehydrogenation System for Liquid Organic Hydrogen Carrier with Enhanced Reaction Rate

Owing to the massive expansion and intermittent nature of renewable power, green hydrogen production, storage, and transportation technologies with improved economic returns need to be developed. Moreover, the slowness of the dehydrogenation reaction is a primary barrier to the commercialization of liquid organic hydrogen carrier (LOHC) technology. The present study focused on increasing the speed of dehydrogenation, resulting in the proposal of a triple-loop dehydrogenation system comprising reaction, heating, and chilling loops. The reactor has a rotating cage containing a packed bed of catalyst pellets, which is designed to enhance both heat and mass transfer by helping to detach precipitated hydrogen bubbles from the catalyst surface. In addition, the centrifugal force aids in isolating the gas phase from the LOHC liquid. A dehydrogenation experiment was conducted using the reaction and chilling loops, which revealed that the average hydrogen production rate during the first hour was 52.6 LPM (liter per minute) from 26.3 L of perhydro-dibenzyl-toluene with 1.5 kg of 0.5 wt% Pt/Al2O3 catalyst. This was approximately 48% more than the value predicted with the reaction kinetics measured with a small-scale plug flow dehydrogenation reactor with less than 1.0 g of 5.0 wt% Pt/Al2O3 catalyst. The concept, construction methods, and results of the preliminary gas infiltration, flow visualization, and reactor pumping experiments are also described in this paper.

Applicability of Single-Layer Graphene as a Hydrogen-Blocking Interlayer in Low-Temperature PEMFCs.

Gas crossover is critical in proton exchange membrane (PEM)-based electrochemical systems. Recently, single-layer graphene (SLG) has gained great research interest due to its outstanding properties as a barrier layer for small molecules like hydrogen. However, the applicability of SLG as a gas-blocking interlayer in PEMs has yet to be fully understood. In this work, two different approaches for transferring SLG from a copper or a polymeric substrate onto PEMs are compared regarding their application in low-temperature PEM fuel cells. The SLG is sandwiched between two Nafion XL membranes to form a stable composite membrane. The successful transfer is confirmed by Raman spectroscopy and in ex situ hydrogen permeation experiments in the dry state, where a reduction of 50% upon SLG incorporation is achieved. The SLG composite membranes are characterized by their performance and hydrogen-blocking ability in a fuel cell setup at typical operating conditions of 80 °C and with fully humidified gases. The performance of the fuel cell incorporating an SLG composite membrane is equal to that of the reference cell when avoiding the direct etching process from a copper substrate, as remnants from copper etching deteriorate the performance of the fuel cell. For both transfer processes, the hydrogen crossover reduction of SLG composite membranes is only 15-19% (1.5 barabs) in the operating fuel cell. Further, hydrogen pumping experiments suggest that the barrier function of SLG impairs the water transport through the membrane, which may affect water management in electrochemical applications. In summary, this work shows the successful transfer of SLG into a PEM and confirms the effective hydrogen-blocking capability of the SLG interlayer. However, the hydrogen-blocking ability is significantly reduced when running the cell at the typical humidified operating conditions of PEM fuel cells, which follows from a combination of reversible interlayer alteration upon humidification and irreversible defect formation upon PEM fuel cell operation.

Uncertainty assessment of aquifer hydraulic parameters from pumping test data

Data from pumping tests is a noisy process, and therefore, performing the pumping test numerous times will not get the same drawdown values. As a consequence, various pumping experiments lead to different values for aquifer parameter estimates. The data of pumping tests are usually analyzed using traditional methods (aquifer tests and AQtesolv software), which depend on trial and error technique. During these methods, non-unique values of hydraulic parameters are selected, which usually have a high level of uncertainty. Uncertainty must be taken into account in determining aquifer parameters, especially when using groundwater models for decision makers. The main goal of this study is to build a comprehensive tool for quantifying uncertainty associated with hydraulic parameter estimation from different pumping test conditions for fully penetrating wells in confined and semi-confined aquifers. To achieve the previous objective, a FORTRAN code was developed to apply the Markov Chain Monte Carlo (MCMC) algorithm using different likelihood functions (exponential, inverse, and log). This developed tool can be used to detect the most probable range of aquifer parameters that are consistent with pumping test data with a high degree of confidence. The tool was successfully used to several hypothetical cases to demonstrate the uncertainty in the quantification of aquifer parameters and compare the findings to the standard method's results. Also, the concept was verified numerically (using Modflow program) with satisfactory results using a hypothetical case with well-known aquifer parameters. Finally, the tool was applied for actual pumping test data with good results.

Optimization of reverse NOE pumping experiments in the analysis of complex systems with densely crowded NMR spectra.

We present an optimization of Reverse NOE-pumping (RNP) in order to observe the 1H signals of ligands bound to proteins. Although various ligand-based NMR screening methods have been proposed, the most frequently used method has been Saturation-Transfer Difference (STD), owing to the relatively easy setup of experiments. Yet the critical point of STD is the selective irradiation of protein without irradiating ligand, and thus the STD technique is unable to observe 1H ligand signals, which resonate across the entire 1H spectral width. In the present study, the RNP experiment has been improved to develop an effective NMR-based screening technique. The optimized RNP spectra reveal less subtraction artifacts and phase distortion than the original RNP spectra, indicating its applicability to any type of ligand molecules.

Observing thermal lensing with quantum light.

The introduction of quantum methods in spectroscopy can provide enhanced performance and technical advantages in the management of noise. We investigate the application of quantum illumination in a pump and probe experiment. Thermal lensing in a suspension of gold nanorods is explored using a classical beam as the pump and the emission from parametric downconversion as the probe. We obtain an insightful description of the behavior of the suspension under pumping with a method known to provide good noise rejection. Our findings are a further step toward investigating the effects of quantum light in complex plasmonic media.

Effect of reduced diameter pipeline and impeller position on the performance of reactor coolant pump

In the reactor coolant pump experiments, there are cases where different impellers are replaced on the same volute for experiments, but due to the different diameter of the impeller inlet, there will be a sudden expansion between the inlet pipeline and the impeller inlet, resulting in a decrease in the efficiency of the pump. In order to solve this problem, a scheme of using an inlet pipe with a reduced diameter structure and changing the position of the impeller was proposed, and based on the three-dimensional incompressible Reynolds N-S equation, the reactor coolant pump device was numerically simulated by CFD software. The data simulation results of the reduced diameter structure, straight pipe flow field and changing the position of the impeller were compared with the model experiments, and the reliability of the calculation results was verified. The results show that the inlet pipe with reduced diameter structure and the method of changing the position of the impeller can effectively solve the problem of efficiency decline caused by the sudden expansion of the flow channel.

Characterization of high-performance nanostructured wick for heat pipes

To investigate the best performance wick forms to support the design and fabrication of high-performance heat pipes. This paper investigates the comprehensive performance of wicks by nanosurface technology and experimental methods to predict heat pipe performance rapidly. In this paper, two kinds of nanostructured wick were prepared by the oxidation-reduction method. They are stainless steel fiber mat-type nanostructured and nickel foam-type nanostructured wicks. The effect of surface nanostructure on the wick performance was investigated by comparing the surface characteristics, capillary properties, permeability, and evaporation properties. In this study, the competitive relationship between the characteristic parameters of the wick is measured by the capillary performance factor M: K/reff, which is used as a measure of the comprehensive performance of the wick, and its maximum value is pursued industrially. The result shows that the nanostructured wick presented excellent super hydrophilic properties. A liquid-lift visualization experimental method for measuring the capillary performance factor M was proposed, and it was verified to be correct by the separation effect of the capillary pumping experiment under a vacuum environment. With the increasing oxidized degree, the densification of nanoparticles on the wick surface increased the capillary performance factor M from 8.68 μm to 13.81 μm, with a maximum enhancement of 59.1%. The effective capillary radius decreased from 47.0 μm to 40.1 μm, with a maximum reduction of 14.9%. The permeability increased from 433 μm2 to 583 μm2, with a maximum enhancement of 34.7%. The increase in porosity made the effective capillary radius dominate the competition for permeability, and the capillary performance factor decreased by 17.1%. The thermal resistance of the wick decreased with the enhancement of the capillary performance factor, which fell from 20.3 cm2·K/W to 12.6 cm2·K/W. The current study provides a reference for the future design and preparation of high-performance heat pipe wicks.

Growth and spectral properties of a novel praseodymium-doped alpha-barium borate laser crystal

A novel Praseodymium-doped borate (Pr:α-BBO) laser crystal was grown successfully by using the Czochralski method. The phase structure, absorption and fluorescence lifetime, as well as blue laser diode (LD) pump performances of Pr:α-BBO were totally studied. The segregation coefficient and valence state of Pr ions in the crystals were investigated using inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy. A 450 nm blue LD was employed to carry out a pump experiment on the Pr:α-BBO slab crystal with a doping concentration of 0.22 at.%. The main emission peaks of Pr3+ ions in the orange-red light band were found to be at 611.5 nm, 634.7 nm, and 638.3 nm. The experimental results show that the Pr:α-BBO crystal exhibits higher orange light fluorescence emission performance, with an emission peak intensity at 611 nm that is 2.1 times stronger than that at 635 nm due to the splitting of the 3P0→3F2 transition (635 nm). By optimizing the Pr:α-BBO laser crystal growth process and further solid-state laser experiments, it can be expected to have broad applications in laser medicine, spectral detection, and nonlinear optical frequency conversion fields.

Performance of Gradient and Gradient-Free Optimizers in Transient Hydraulic Tomography.

Sub-surface characterization in fractured aquifers is challenging due to the co-existence of contrasting materials namely matrix and fractures. Transient hydraulic tomography (THT) is proved to be an efficient and robust technique to estimate hydraulic (Km, Kf) and storage (Sm, Sf) properties in such complex hydrogeologic settings. However, performance of THT is governed by data quality and optimization technique used in inversion. We assessed the performance of gradient and gradient-free optimizers with THT inversion. Laboratory experiments were performed on a two-dimensional, granite rock (80 cm × 45 cm × 5 cm) with known fracture pattern. Cross-hole pumping experiments were conducted at 10 ports (located on fractures), and time-drawdown responses were monitored at 25 ports (located on matrix and fractures). Pumping ports were ranked based on weighted signal-to-noise ratio (SNR) computed at each observation port. Noise-free, good quality (SNR > 100) datasets were inverted using Levenberg-Marquardt: LM (gradient) and Nelder-Mead: NM (gradient-free) methods. All simulations were performed using a coupled simulation-optimization model. Performance of the two optimizers is evaluated by comparing model predictions with observations made at two validation ports that were not used in simulation. Both LM and NM algorithms have broadly captured the preferential flow paths (fracture network) via K and S tomograms, however LM has outperformed NM during validation ( ). Our results conclude that, while method of optimization has a trivial effect on model predictions, exclusion of low quality (SNR ≤ 100) datasets can significantly improve the model performance.

Electrically Tunable Nonlinearity at 3.2 Terahertz in Single-Layer Graphene.

Graphene is a nonlinear material in the terahertz (THz) frequency range, with χ(3) ∼ 10-9 m2/V2 ∼ 15 orders of magnitude higher than that of other materials used in the THz range, such as GaAs or lithium niobate. This nonlinear behavior, combined with ultrafast dynamic for excited carriers, proved to be essential for third harmonic generation in the sub-THz and low (<2.5 THz) THz range, using moderate (60 kV/cm) fields and at room temperature. Here, we show that, for monochromatic high peak power (1.8 W) input THz signals, emitted by a quantum cascade laser, the nonlinearity can be controlled using an ionic liquid gate that tunes the graphene Fermi energy up to >1.2 eV. Pump and probe experiments reveal an intense absorption nonlinearity at 3.2 THz, with a dominant 3rd-order contribution at EF > 0.7 eV, hence opening intriguing perspectives per engineering novel architectures for light generation at frequencies > 9 THz.

Tm:CALGO lasers at 2.32 µm: cascade lasing and upconversion pumping.

We report on the first laser operation of a disordered Tm:CaGdAlO4 crystal on the 3H4 → 3H5 transition. Under direct pumping at 0.79 µm, it generates 264 mW at 2.32 µm with a slope efficiency of 13.9% and 22.5% vs. incident and absorbed pump power, respectively, and a linear polarization (σ). Two strategies to overcome the bottleneck effect of the metastable 3F4 Tm3+ state leading to the ground-state bleaching are exploited: cascade lasing on the 3H4 → 3H5 and 3F4 → 3H6 transitions and dual-wavelength pumping at 0.79 and 1.05 µm combining the direct and upconversion pumping schemes. The cascade Tm-laser generates a maximum output power of 585 mW at 1.77 µm (3F4 → 3H6) and 2.32 µm (3H4 → 3H5) with a higher slope efficiency of 28.3% and a lower laser threshold of 1.43 W, out of which 332 mW are achieved at 2.32 µm. Under dual-wavelength pumping, further power scaling to 357 mW at at 2.32 µm is observed at the expense of increased laser threshold. To support the upconversion pumping experiment, excited-state absorption spectra of Tm3+ ions for the 3F4 → 3F2,3 and 3F4 → 3H4 transitions are measured for polarized light. Tm3+ ions in CaGdAlO4 exhibit broadband emission at 2.3 - 2.5 µm making this crystal promising for ultrashort pulse generation.

Thermal balance and gap flow of high-pressure, large-scale plunger pairs

Fitting gaps are a critical factor affecting the efficiency of high-pressure, large-scale plunger pumps. In actual work, fitting gaps change under liquid pressure and temperature rise, and the fluid flow in the annular channel changes under the fitting gap, in turn affecting the fitting gap. Therefore, on the basis of the thermo-fluid–structure interaction, a thermodynamic analysis model of plunger friction pairs is established in this work. The model considers the heat production due to plunger pair friction, frictional head loss, local head loss and heat dissipation caused by the fluid and air. Given that heat production and dissipation are greatly affected by annular channel flow, the deformation and leakage equations of the large-scale annular channel are established on the basis of pressure and temperature rise. In consideration of the gap deformation, gap flow, heat production, and heat dissipation of the plunger, a thermal balance equation is established, and the temperature rise of the plunger pair under different initial gaps is analyzed. In addition, a plunger pump experiment system is built to test the temperature rise of the plunger pair. Results show that the model can effectively predict the temperature of the plunger friction pair. The research results can provide a theoretical basis for the design of large-scale, high-pressure gap seals.

Developing a real-world scenario to foster learning and working 4.0 – on using a digital twin of a jet pump experiment in process engineering laboratory education

ABSTRACT A newly-developed online laboratory experiment in immersive virtual reality (VR) is used for process engineering students. A digital twin (DT) of a jet pump was realised using the game engine Unreal Engine 4. The chance was taken for an instructional redesign deviating from the conventional cookbook-experiment to better integrate the changing competence demands of the working world 4.0 (W4.0). A real-world scenario (RWS) is used to address the sometimes-vague problem-solving assignments of W4.0: the students found themselves in an ambiguous situation which must be cleared and resolved constructively and autonomously by them. The RWS was evaluated by triangulating qualitative and quantitative methods. Firstly, its Constructive Alignment was evaluated, i.e. whether the intended learning outcomes to be achieved through the novel teaching and learning activities were reflected in the assessment tasks, too. Secondly, students were surveyed regarding their attitudes towards such new forms of laboratory learning. The results show that even if the students initially seem overwhelmed by the unfamiliar type of assignment, they are nevertheless able to solve the work-related engineering problem – at least with varying degrees of assistance from a fictional immediate superior. The students appreciate the opportunity to think creatively and independently develop solutions to the assignment.

Strongly Correlated Exciton-Magnetization System for Optical Spin Pumping in CrBr3 and CrI3 .

Ferromagnetism in van der Waals systems, preserved down to a monolayer limit, attracted attention to a class of materials with general composition CrX3 (X=I, Br, and Cl), which are treated now as canonical 2D ferromagnets. Their diverse magnetic properties, such as different easy axes or varying and controllable character of in-plane or interlayer ferromagnetic coupling, make them promising candidates for spintronic, photonic, optoelectronic, and other applications. Still, significantly different magneto-optical properties between the three materials have been presenting a challenging puzzle for researchers over the last few years. Herewith, it is demonstrated that despite similar structural and magnetic configurations, the coupling between excitons and magnetization is qualitatively different in CrBr3 and CrI3 films. Through a combination of the optical spin pumping experiments with the state-of-the-art theory describing bound excitonic states in the presence of magnetization, weconcluded that the hole-magnetization coupling has the opposite sign in CrBr3 and CrI3 and also between the ground and excited exciton state. Consequently, efficient spin pumping capabilities are demonstrated in CrBr3 driven by magnetization via spin-dependent absorption, and the different origins of the magnetic hysteresis in CrBr3 and CrI3 are unraveled.

X-ray free electron laser studies of electron and phonon dynamics of graphene adsorbed on copper

We report optical pumping and x-ray absorption spectroscopy experiments at the Pohang Accelerator Laboratory free electron laser that probes the electron dynamics of a graphene monolayer adsorbed on copper in the femtosecond regime. By analyzing the results with ab initio theory we infer that the excitation of graphene is dominated by indirect excitation from hot electron-hole pairs created in the copper by the optical laser pulse. However, once the excitation is created in graphene, its decay follows a similar path as in many previous studies of graphene adsorbed on semiconductors, i.e., rapid excitation of strongly coupled optical phonons and eventual thermalization. It is likely that the lifetime of the hot electron-hole pairs in copper governs the lifetime of the electronic excitation of the graphene.Received 21 November 2022Accepted 26 January 2023DOI:https://doi.org/10.1103/PhysRevMaterials.7.024005©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectron emissionPhysical SystemsGrapheneTechniquesMolecular dynamicsX-ray absorption spectroscopyCondensed Matter, Materials & Applied Physics