Yao Yang

Interfacial water structure is theoretically envisioned as the master regulator of electrocatalytic reaction kinetics, but the direct experimental validation of this role has remained a formidable challenge. Probing kinetic isotope effects (KIEs) is paramount to deciphering the elusive proton-coupled electron transfer (PCET) mechanisms in alkaline media, a long-standing enigma in electrocatalysis. Such precision, however, demands the uncompromising rigor of atomic-level-precise single-crystal electrodes and ultrapure D2O to ensure definitive results. Here, we uncover a hydrogen evolution reaction KIE that varies sharply with the surface structure: ∼6 for Pt(100), ∼1 for Pt(111), and intermediate values for Pt(110). Through a combination of nuclear–electronic orbital density functional theory (NEO-DFT) and in situ laser-induced temperature-jump (LITJ) experiments, we propose that this disparity originates from the difference between a rigid, hexagonal H-bonded network on Pt(111) and a more disordered, flexible interfacial layer on Pt(100) that would be more sensitive to isotopic substitution, as well as from differences in H/D adsorption sites, which would influence the effective proton transfer distances. Furthermore, measurements with stepped surfaces show that step density acts as a critical dial to tune these water environments. Finally, to bridge the knowledge gap between bulk single-crystals and practical nanoparticles, {100}-oriented Pt nanocubes and {111}-oriented Pt nanotetrahedrons reveal a facet-dependent KIE trend comparable to their single-crystal counterparts. These insights provide a transformative framework for the rational design of high-performance interfaces for green hydrogen production.

Electrochemical CO2 reduction (CO2RR) offers a promising strategy to convert CO2 into high-value chemicals and fuels. However, probing the mechanism of dynamic catalyst reconstruction remains a longstanding challenge, which calls for operando time-resolved and quantitative spectroscopic methods. Here, we employed operando high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) to monitor real-time structural evolution of bimetallic FeCu single-atom catalysts (SACs) on nitrogen-doped carbon (FeCu–N–C) as a model single-atom catalyst for the CO2RR. FeCu–N–C exhibits a 2-fold increase in Faradaic efficiency for CO formation and an order-of-magnitude enhancement in the CO partial current density at the same applied potential, when compared to monometallic Fe SAC (Fe–N–C). To elucidate the origin of this performance enhancement, operando HERFD-XAS was used to directly probe the dynamic evolution of metal oxidation states and coordination environments under operating conditions, revealing a dynamic reconstruction of isolated Fe and Cu single atoms into catalytically active metallic clusters. In contrast, the Fe SAC control remains atomically dispersed over the course of CO2RR. The atomic-scale structural insights are further corroborated by aberration-corrected scanning transmission electron microscopy. These findings shed light on the synergistic role of Cu in modulating the dynamic reconstruction of single-atom Fe sites and provide fundamental insights for the rational design of high-performance single-atom catalysts for CO2 electroreduction.

Operando measurements have rapidly expanded the scope of electrocatalysis by enabling direct observation of catalytic interfaces under working conditions and by linking structural, compositional, and spectroscopic observables to activity and selectivity. However, the growth of operando methods has outpaced the adoption of broadly shared experimental standards, creating persistent challenges in reproducibility, interpretation, and comparison across laboratories and platforms. This perspective synthesizes discussions from the 2025 National Science Foundation Workshop on Rigor and Reproducibility in Electrocatalysis and outlines a practical framework for the rigorous use of operando measurements in electrocatalysis. We highlight three recurring needs: careful implementation of complex methods to avoid overinterpretation; recognition that (subtle) differences in reactor architecture, hydrodynamics, and electrical boundary conditions can alter apparent kinetics and selectivity; and transparent reporting standards that enable meaningful cross-comparison without constraining measurement-specific cell innovation. Focusing on widely used techniques (including X-ray and vibrational spectroscopies, mass spectrometry, and electron microscopy), we discuss technique-specific pitfalls, cross-validation strategies, and recurring platform-agnostic considerations such as mass transport, current distribution, temporal-resolution mismatches, and catalyst evolution. This Perspective aims to strengthen the mechanistic inference and improve the reproducibility, comparability, and predictive value of operando electrocatalysis research.

We present direct experimental evidence of dynamic evolution from single-atom catalysts to Cu nanostructures rich in active nanograins, based on a conductive metal–organic framework-based Cu single-atom catalyst (Cu-SAC). Operando synchrotron-based high-energy-resolution X-ray spectroscopy and IR absorption spectroscopy quantitatively tracked the structural and molecular fingerprints during single-atom-to-nanograin evolution. Operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) directly captured real-time movies of dynamic structure evolution from isolated Cu single atoms to metallic Cu nanograins under the CO2RR. Operando electrochemical four-dimensional (4D) STEM reveals the complex polycrystalline Cu nanostructures rich in metallic nanograin boundaries, serving as catalytically active sites. This study paves the way for the design of a new generation of single-atom catalysts based on their operando active structures instead of pristine structures.

The rapid increase in atmospheric carbon dioxide (CO₂) is a primary driver of climate change. However, current CO₂ conversion and storage technologies remain inefficient, energy-intensive, and costly, limiting their widespread implementation. Electrochemical CO₂ conversion offers a promising alternative as it operates under ambient conditions, does not require hazardous reagents, and can be powered by renewable energy.

Lithium metal-based batteries have been recognized as the next-generation high performance lithium battery technologies. However, uncontrolled lithium dendrite growth and a lack of fundamental understanding of the complex solid-electrolyte interphase (SEI) evolution dynamics remain as significant challenges. While ex situ methods have provided a baseline understanding, modern operando methods, particularly scanning transmission electron microscopy (STEM) [1], have provided extraordinarily valuable insights for a mechanistic understanding of dynamic battery interfaces.

Water electrolysis is a promising method of clean electrochemical hydrogen production and a critical component of the global sustainable energy initiative. The overall reaction can be decoupled into the 2e^– hydrogen evolution reaction (HER) and the kinetically sluggish 4e^– oxygen evolution reaction (OER). Developing efficient and cost-effective OER catalysts is therefore necessary for industrial viability. One approach to performance optimization is tuning the ratios of non-precious metal oxides in the catalyst structure.¹ While commercial ruthenium oxide is comparable in activity to industrially-used catalysts, cobalt and barium inclusions have the potential to dramatically increase activity while reducing use of precious metals.

The development of electrocatalysts which combine low-cost with high activity and durability for the Oxygen Evolution Reaction (OER) is crucial for the manufacturing and maintenance of cost-effective water electrolysers. Transition metal oxide catalysts have the prospect of providing similar performance as conventional precious metal at substantially lower cost. Among them, RuO₂ stands out as a benchmark catalyst for OER due to its excellent stability in alkaline media and good catalytic activity. To design advanced transition metal oxide catalysts, a fundamental understanding of the interdependence of catalyst structure and composition with reactivity and durability is required.

I will present our recent progress in probing dynamic structural evolution of energy materials by developing multimodal operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) and synchrotron-based high-energy-resolution X-ray spectroscopy to across multiple spatiotemporal scales.[1-3] Operando electrochemical 4D-STEM in liquid, assisted by machine learning, has shown great potential to interrogate complex structures of active sites of energy materials at solid-liquid interfaces. My group recently employed operando electrochemical 4D-STEM to provide the first direct nanoscale movies visualizing evolution from single-atom catalysts to active Cu nanostructures for CO₂ reduction to liquid fuels.[4] I will then introduce our instrument development on the first-of-its-kind operando heating and cooling EC-STEM to diagnose battery failure mechanisms below freezing temperatures and catalyst degradation mechanisms at elevated temperatures. [5]