Despite being capable of very fast charging, the pseudocapacitive properties of electrochemical capacitors still require significant research to attain energy densities comparable to that of batteries. Herein we discuss and theoretically benchmark the physics of quantized capacitance as a Faradaic charge storage mechanism, providing near “ideal” pseudocapacitive properties in the context of batterylike energy storage. Through careful electrolyte and reactant engineering, our physical analysis suggests that this less explored “pseudocapacitive battery” mechanism could provide power densities of approximately ${10}^4$ W/L combined with volumetric energy densities in the range of 100 Wh/L (or potentially greater). These benchmarks are arrived at though a comprehensive analysis of two-dimensional (2D) graphitic nanoparticles considering the impact of solvation, electron-electron interactions, and electron transfer processes. In general, our findings indicate that 2D nanomaterials exhibiting quantized capacitance provide a promising and underexplored physical axis within electrochemical capacitors towards realizing very fast charging at energy densities comparable to that of batteries.

The atmospheric concentration of methane has more than doubled since the start of the Industrial Revolution. Methane is the second-most-abundant greenhouse gas created by human activities and a major driver of climate change. This APS-Optica report provides a technical assessment of the current state of monitoring U.S. methane emissions from oil and gas operations, which accounts for roughly 30% of U.S. anthropogenic methane emissions. The report identifies current technological and policy gaps and makes recommendations for the federal government in three key areas: methane emissions detection, reliable and systematized data and models to support mitigation measures, and effective regulation.

Hot electrons generated from the decay of localized surface plasmons in metallic nanostructures have the potential to transform photocatalysis, photodetection, and other optoelectronic applications. However, the understanding of hot-carrier generation in realistic nanostructures, in particular the relative importance of interband and intraband transitions, remains incomplete. Here we report theoretical predictions of hot-carrier generation rates in spherical nanoparticles of the noble metals silver, gold, and copper with diameters up to 30 nm consisting of more than one million atoms obtained from an atomistic linear-scaling approach. As the nanoparticle size increases, the relative importance of interband transitions from $d$ bands to $sp$ bands relative to surface-enabled $sp$-band to $sp$-band transitions increases. We find that the hot-hole generation rate is characterized by a peak at the onset of the $d$ bands, while the position of the corresponding peak in the hot-electron distribution can be controlled through the illumination frequency. In contrast, intraband transitions give rise to hot electrons, but relatively cold holes. Importantly, increasing the dielectric constant of the environment removes hot carriers generated from interband transitions, while increasing the number of hot carriers from intraband transitions. The insights resulting from our work enable the design of nanoparticles for specific hot-carrier applications through their material composition, size, and dielectric environment.

Understanding the interfacial reactivity of aqueous electrolytes is crucial for their use in future batteries. We investigate the reactivity of the bis(trifluoromethane)sulfonimide anion when exposed to a strongly basic medium, by means of ab initio molecular dynamics and enhanced sampling techniques. In particular, we study the nucleophilic attack by the hydroxide anion, which was proposed as a mechanism for the formation of the solid electrolyte interphase at the negative electrode with water-in-salt electrolytes. While in the gas phase we recover a stable gaseous product, namely fluoroform, we observe the formation of trifluoromethanol in strong basic conditions, which then rapidly deprotonates to form ${\mathrm{CF}}_3{\mathrm{O}}^{-}$. This anion was suggested recently as a key compound leading to the formation of a solid electrolyte interphase on an $\mathrm{Si}$-C anode. Such an approach could be leveraged to discover convenient additives leading to the formation of a stable interphase.

With the rapidly improving efficiency and stability of perovskite solar cells, the transition of small area device fabrication innovations into modules is becoming increasingly important for the commercialization of this technology. The record efficiencies of small perovskite cells are already approaching that of the best silicon crystal solar cells, but the module efficiencies are still far behind. Understanding the factors that cause the cell-to-module (CTM) efficiency loss is critical for large area perovskite module development. Here, we experimentally validate a comprehensive model that analyzes the CTM efficiency loss with a precision better than 97%. Using the model, we decipher the impact of the critical module components and fabrication variables, including perovskite band gap, transparent electrodes, scribing lines, and film uniformity, on module aperture efficiency. Our analysis provides pathways toward the aperture efficiency ceiling of 25.8% for single-junction perovskite solar modules with a band gap of 1.49 eV. Enlightened by the model, we find that tandem structures have intrinsic merit to achieve high efficiency perovskite modules of 28.4% with a much lower CTM derate due to the smaller photocurrent but larger photovoltage.

Capacitance measurements as a function of voltage, frequency, and temperature are a useful tool to gain a deeper insight into the electronic properties of semiconductor devices in general and of solar cells in particular. Techniques such as capacitance-voltage, Mott-Schottky analysis, or thermal-admittance spectroscopy measurements are frequently employed in perovskite solar cells to obtain relevant parameters of the perovskite absorber. However, state-of-the-art perovskite solar cells use thin electron- and hole-transport layers to improve the contact selectivity. These contacts are often quite resistive in nature, which implies that their resistance will significantly contribute to the total device impedance and thereby also affect the overall capacitance of the device, thus partly obscuring the capacitance signal from the perovskite absorber. Based on this premise, we develop a simple multilayer model that considers the perovskite solar cell as a series connection of the geometric capacitance of each layer in parallel with their voltage-dependent resistances. Analysis of this model yields fundamental limits to the resolution of spatial doping profiles and minimum values of doping and trap densities, built-in voltages, and activation energies. We observe that most of the experimental capacitance-voltage-frequency-temperature data, calculated doping and defect densities, and activation energies reported in the literature are within the derived cutoff values, indicating that the capacitance response of the perovskite solar cell is indeed strongly affected by the capacitance of its selective contacts.

The large variability of renewable power sources is a central challenge in the transition to a sustainable energy system. Electricity markets are central for the coordination of electric power generation. These markets rely evermore on short-term trading to facilitate the balancing of power generation and demand and to enable systems integration of small producers. Electricity prices in these spot markets show pronounced fluctuations, featuring extreme peaks as well as occasional negative prices. In this article, we analyze electricity price time series from the European Power Exchange market, in particular the hourly day-ahead, hourly intraday, and 15-min intraday market prices. We quantify the fluctuations, correlations, and extreme events and reveal different time scales in the dynamics of the market. The short-term fluctuations show remarkably different characteristics for time scales below and above 12 h. Fluctuations are strongly correlated and persistent below 12 h, which contributes to extreme price events and a strong multifractal behavior. On longer time scales, they get anticorrelated and price time series revert to their mean, witnessed by a stark decrease of the Hurst coefficient after 12 h. The long-term behavior is strongly influenced by the evolution of a large-scale weather pattern with a typical time scale of four days. We elucidate this dependence in detail using a classification into circulation weather types. The separation in time scales enables a superstatistical treatment, which confirms the characteristic time scale of four days, and motivates the use of $q$-Gaussian distributions as the best fit to the empiric distribution of electricity prices.

The established theory of a two-dimensional (2D) Wannier exciton in a uniform electric field is used to analyze the electroabsorption response of an archetypal 2D metal halide perovskite (MHP), phenethylammonium lead iodide. The high level of agreement between the electroabsorption simulation and measurement allows for a deepened understanding of the redshift of exciton energy, according to the quadratic Stark effect, and the continuum wave function leaking, according to the Franz-Keldysh effect. We find the field dependency of each of these effects to be rich with information, yielding measurements of the exciton Bohr radius, transition dipole moment, polarizability, and reduced effective mass of the exciton. Most importantly, the band-gap energy and exciton binding energy are unambiguously determined with 1σ variance of 4 meV. The high precision of these new measurement methods opens the opportunity for determining the influence of chemical and environmental factors on the optoelectronic properties of MHPs, which would enable the fabrication of highly efficient and reproducible light-harvesting and light-emitting optoelectronic devices.