Energy Technologies

Drawing on existing market designs with independent resource participation in electricity markets, this study analyzes participation models for hybrid resources combining renewable generation and storage. Two models are considered: in the first, the components operate independently, with the Independent System Operator (ISO) managing the storage state of charge (SoC); in the second, the hybrid resource acts as an integrated unit, submitting offers as a “black box” and managing its SoC internally. Using a production cost model for the zonal New York Bulk Power System, we evaluate trade-offs in system reliability, market efficiency, and asset profitability. Our results provide several key insights for policymakers, showing that the ISO-managed granular model enhances social welfare through explicit SoC management, while the simpler integrated model is more computationally efficient, but may cause more real-time violations and lower overall profits.

Increasing growth of distributed solar photovoltaics (PV) and electric vehicles (EV) can strain local distribution networks and require costly upgrades. Distributed battery storage, often deployed alongside PV, can be used to mitigate those costs, depending on how batteries are operated. This study evaluates the potential deferral value of distributed battery storage across a range of tariff structures, focusing on the rate structures most commonly available to residential customers today and related variants. Deferrals are evaluated with a least-cost distribution grid expansion optimization model to identify requirements on line reconductoring, transformer upgrades, and voltage regulator installations under each tariff. Results show that TOU rates and net billing tariffs can yield meaningful deferral value, depending on specific tariff structure features. Under the best performing tariff structure tested, storage produced a median annualized deferral value of $7.18 per kW of storage capacity ( kW S ) across all feeders in the sample, though deferral values were considerably larger for feeders with peak loads that coincide with utility system peak, i.e., timing of TOU peak period. In contrast, under an unrestricted TOU design with no restrictions on grid charging or discharging, the median deferral value was $0/ kW S illustrating the critical importance of tariff structure details.

A mathematical framework for simulating the impedance response of a proton-exchange-membrane fuel cell (PEMFC) was developed to provide insight into the coupled physics and chemistry that influence observed spectra. The model was based on a cell-level continuum model that was linearized and represented in the frequency domain, which allowed for the accounting of coupled transport in a PEMFC and the simulation of full spectra in seconds. Good agreement was observed between experimental and simulated polarization and impedance data. Consistency between steady-state and frequency-domain continuum models was confirmed, which allowed for the extraction of kinetic information from the experimental impedance spectra. The model framework was used to estimate contributions associated with ohmic, charge-transfer, and transport resistances, which was shown to align with power-loss voltage breakdown analyses of steady-state simulations. A proposed equivalent-circuit model facilitated estimates of the low-frequency impedance, which can be used in conjunction with the impedance model to assess properties of the electrochemical cell. Since the model accounted for the effects of coupled physics, pressure impedance transfer functions were simulated, which showed quantitative agreement with experimental observations from literature.

ABSTRACT Achieving high‐energy‐density and long‐term cycling stability in Mn‐redox‐based cathodes is a critical step toward advancing Ni‐ and Co‐free Li‐ion chemistries to diversify supply chains and lower battery costs. Here, we demonstrate an unusually high performance benchmark for Mn‐redox cathodes using near‐micron single‐crystalline δ‐phase cation‐disordered rocksalt (δ‐DRX), derived from Mn‐rich DRX, delivering ≈640 Wh kg −1 with ≈97% capacity retention over 400 cycles. The very high energy density and cycle life were achieved by using a high Mn content, to suppress oxygen redox activity, and careful control of the synthesis parameters to tune single crystal particle size. Using high‐throughput automated electron microscopy, we identify interparticle compositional heterogeneity present in the early stage of phase‐pure DRX formation as the origin of orthorhombic LiMnO 2 impurity formation during cooling, a finding that rationalizes the long high‐temperature dwell times required and the associated particle coarsening in conventional synthesis. We demonstrate that an accelerated cooling strategy kinetically suppresses localized impurity formation, reducing long high‐temperature exposure, and enables downsizing of single‐crystalline Mn‐rich DRX particles to the near‐micron regime (D50 = 1.5 µm). This work provides a mechanistic basis for particle‐size control in Mn‐rich DRX synthesis, and presents δ‐DRX as a stable, sustainable, high‐performance, Ni‐ and Co‐free cathode material.

Abstract Catalytic activity and electrical conductivity are critical to the performance of electrocatalysts and electrochemical devices, yet their combined assessment under operating conditions remains challenging. Here, we introduce operando Fourier-transform electrochemical source–drain impedance spectroscopy (FT-ESDIS), which simultaneously measures catalyst-film conductivity and charge-transfer resistance (Rct) with high temporal resolution at high current densities. During Fe incorporation into nickel (oxy)hydroxide (NiOxHy), FT-ESDIS revealed that catalytic activation and charge transport properties evolve on distinct time scales, demonstrating that activity alone cannot capture catalyst-layer evolution during operation. At higher overpotentials, nickel-containing (oxy)hydroxides (Ni(Fe)OxHy) showed an abrupt apparent conductivity increase upon oxidation, with conductivity remaining nearly unchanged thereafter, whereas iron (oxy)hydroxide (FeOxHy) exhibited a gradual increase in apparent conductivity. Previous reports attributed this overpotential-dependent increase to the formation of high-valent Fe species. However, we show that the increase arises predominantly from an electrolyte-mediated current artifact, in which a potential perturbation at one electrode changes the local solution potential at the neighboring electrode surface and modulates its Faradaic current, producing an apparent conductivity response without direct through-film transport. We further establish a quantitative relationship between this artifact and Rct, enabling its estimation and subtraction from the apparent conductivity. The corrected FeOxHy conductivity exhibits substantially weaker potential dependence, suggesting that charge transport involving high-valent Fe species, if present, contributes much less than inferred from the uncorrected response. By resolving kinetic and transport properties under operating conditions, FT-ESDIS provides a more comprehensive basis for interpreting electrocatalyst behavior and establishes transport and reactivity as complementary descriptors for electrochemical energy-conversion systems.

We report the effect of reverse polarization on thin-film Ni(Fe)OOH anodes in conditions that mirror those seen in commercial alkaline water electrolyzer stacks. Regardless of the extent of the reverse polarization potential, the anodic charge capacity decreases over successive cycles, indicating loss of active Ni2+/Ni3+ sites. Electrodes held for a longer period in the reduced state exhibited an accelerated catalyst loss through dissolution and structural reorganization during reverse polarization. In situ Raman spectroscopy and X-ray photoelectron spectroscopy revealed a significant decrease in the Fe:Ni surface ratio after reverse polarization, which correlates with a measurable decline in activity toward the oxygen evolution reaction. These findings illustrate how nickel iron oxyhydroxide anodes degrade during reverse polarization conditions and how managing the dissolved ions in the recirculating KOH improves anode lifetimes.

Directly monitoring the structure and evolution of an electrode surface during reaction provides uniquely powerful insight into interfacial processes. Electrochemical atomic force microscopy (EC-AFM) and Scanning Tunneling Microscopy (EC-STM) have therefore become essential tools for linking potential-controlled surface transformations to macroscopic current and product outcomes. In EC-AFM, surface features are measured from the deflection of a typically laser-tracked cantilever, enabling imaging of metals, semiconductors, and insulators in liquid electrolytes. By selecting appropriate probes and operating modes, EC-AFM maps topography together with complementary channels such as mechanical response, friction, and local electrical contrast, offering a multi-parametric view of the electrified interface during processes such as film formation, corrosion, gas evolution, and electrodeposition. By contrast, EC-STM measures the tunneling current between a conductive tip and a conductive substrate, providing access to atomic-scale surface order, reconstruction, and adsorbate structures under EC control. In liquid environments, STM performance is limited by parasitic faradaic currents and capacitive coupling, making careful EC configuration and robust tip insulation (coated everywhere except the apex) critical for stable imaging. This tutorial summarizes practical EC cell considerations, probe preparation, alignment and calibration steps, and data-handling best practices for acquiring reproducible in-operando SPM datasets. This tutorial seeks to make EC-AFM/EC-STM measurements more approachable for beginners by clearly explaining the fundamental principles as well as practical considerations, allowing practitioners to gain highly informative EC insights on their systems of interest. Throughout, we emphasize common EC artifacts and decision rules that help newcomers distinguish true potential-dependent surface dynamics from drift, bubble interference, leakage currents, and feedback-induced contrast, enabling reliable interpretation of AFM/STM observations in EC environments.

Cation-disordered rock-salt (DRX) oxides have emerged as a promising class of high energy density cathodes for next-generation lithium-ion batteries. Fluorination has been widely employed to tune the redox chemistry and structural stability of these materials, leading to enhanced electrochemical performance. However, the degradation mechanisms of fluorinated DRX (F-DRX) cathodes during electrochemical cycling remain poorly understood. Here, we investigate the degradation behavior of an F-DRX cathode cycled in a conventional carbonate-based electrolyte and a localized high-concentration electrolyte (LHCE). By correlating electrochemical performance with interfacial and bulk structural evolution, we elucidate the role of electrolyte chemistry and deep discharge voltage in governing structural transformation and degradation. The results reveal more pronounced surface and bulk structural changes in the conventional LiPF6-carbonate electrolyte relative to LiFSI-LHCE, indicating accelerated degradation in the former. Lowering the discharge cutoff voltage from 2.0 to 1.5 V further promotes interfacial degradation in both electrolyte systems. This work demonstrates that the LHCE offers superior compatibility with F-DRX cathodes, enabling stable cycling by mitigating surface and bulk structural degradation. These insights clarify the interplay between electrolyte chemistry and voltage window in F-DRX degradation and highlight the critical importance of advanced electrolyte designs for unlocking the full potential of DRX cathodes.

The rising demand for hydrogen calls for improvements in the efficiency of liquid alkaline water electrolysers (LAWEs), which can be fulfilled by advanced electrodes or separators. Nevertheless, they also intensify hydrogen crossover and safety concerns, thus mandating efficient mitigation strategies. Here we studied the correlation between cathodes and hydrogen crossover behaviours and mitigated safety risks by designing a gas recombination catalyst (GRC). We attribute the elevated hydrogen crossover associated with platinum-based cathodes to their preferential utilization for the hydrogen evolution reaction that creates elevated hydrogen supersaturation, as evidenced by direct measurements of dissolved hydrogen concentration. Varying the placement of platinum layers relative to the cathode–separator interface also supports this conclusion. The implementation of a GRC reduces hydrogen crossover by 95% without affecting LAWE performance and functions for over 1,000 h at 1 A cm−2. This study provides insights into hydrogen supersaturation and the crossover mechanism, as well as offering a promising pathway to enhance the efficiency and reliability of alkaline water electrolysis.