Jun Cai

Resolving the mechanistic link between local coordination environments and dynamic surface restructuring is essential for advancing carbon dioxide activation and hydrogenation on copper-based catalysts. Here, we demonstrate that the configuration of steps and terraces governs the restructuring pathways on high-index Cu(hkl) surfaces with varying (111) × (100) step densities by integrating in situ spectroscopy/microscopy and theoretical simulation. On the Cu(211) surface [3(111) × (100)], low-coordinated step sites facilitate CO2 activation and the subsequent reaction-driven fragmentation of Cu into nanoclusters. These metastable ensembles serve as active sites that stabilize key intermediates─formate and methoxy─thereby driving sequential hydrogenation. In contrast, on the Cu(557) surface featuring a lower step density [6(111) × (100)], oxygen atoms derived from CO2 dissociation at step sites migrate onto the terraces, assembling into ordered oxide chains that passivate the active sites. Our findings reveal that modulating the step density could effectively dictate the surface reconstruction and the reaction activity of carbon dioxide hydrogenation over Cu-based catalysts.

Acquiring information on the evolution of chemical states and real-space morphological changes under identical reaction conditions is crucial for elucidating the mechanisms of heterogeneous catalytic reactions. In this study, we design and implement a microreactor with high electron transparency, enabling correlated in situ x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) measurements for the same type of sample under identical reaction environments, while integrating online mass spectrometry for seamless coupling of spectroscopic and imaging data. This advancement allows direct correlation between the in situ chemical-state information obtained by XPS and the real-space structural evolution captured by TEM. Using the oxidation–reduction process of Ni nanoparticles in O2/H2 atmospheres as a model reaction, we systematically investigate the dynamic relationship between surface chemical states and morphological reconstruction from near-ambient to ambient pressures, demonstrating the stability and applicability of the microreactor under complex gas environments. This work provides a new experimental approach for mechanistic studies of gas–solid interfacial reactions under realistic operating conditions and establishes a methodological foundation for the rational design and optimization of high-performance catalysts.

Ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) is a rapidly developing technique with broad applications in surface science, catalysis, energy materials, and environmental science. In this study, we present a laboratory-based AP-XPS system that integrates the de Laval nozzle technology to generate a supersonic gas jet. The gas jet creates an ultrathin high-pressure (up to 1 bar) region directly above the sample surface, enabling XPS measurements at 1 bar with a laboratory-based AP-XPS system. The surface pressure was validated by using both a custom-built offline pressure measurement system and computational fluid dynamics simulations. Owing to its limited thickness (∼20 μm), this high-pressure region effectively minimizes gas–electron scattering under elevated pressures. Moreover, the gas delivery design establishes a localized low-pressure zone near the front cone, significantly reducing the load on the differential pumping stage. The method achieves XPS measurements at 1 bar, enhancing a laboratory-based AP-XPS platform for true ambient pressure characterization under certain industrially relevant catalytic conditions.

Ammonia (NH₃) is a principal carbon-free hydrogen (H₂) carrier, yet its decomposition via conventional thermocatalysis is restricted by kinetically demanding high temperatures. Integrating the reaction with in situ product removal to achieve high decomposition efficiency under mild conditions presents a formidable challenge. Here, we report a plasma-enhanced dual-membrane ammonia decomposition system (PEDMADS) that synergistically couples dielectric barrier discharge (DBD), a highly dispersed atomic layer deposition (ALD)-synthesized Ru/SiO₂ catalyst, and an integrated ultrathin Pd membrane (1.8 μm) to enable a high H₂ space-time yield of 1567 mmol g^-1 h^-1 at 400 °C. Furthermore, a downstream cascade of high-performance Silicalite-1 (S-1) membranes achieved energy-efficient NH₃ recovery, exhibiting unprecedented NH₃/H₂ and NH₃/N₂ separation factors of 686 and 7076 under ambient conditions. Molecular dynamics simulations revealed this selectivity arose from a preferential adsorption-driven molecular sieving mechanism. The five-stage cascade reduced the effluent NH₃ concentration from 24.1% to below 4%, achieving 87% removal efficiency. Techno-economic analysis indicated a levelized cost of 0.92 $/kg H₂ with a 95.9% carbon footprint reduction compared to the conventional thermal process, thus offering a compelling blueprint for a sustainable ammonia-hydrogen economy.

The catalytic versatility of the copper surface calls for a fundamental understanding of the formation and reactivity of key intermediates in various C₁ catalytic conversions such as water-gas shift reaction, CO/CO₂ hydrogenation, and electrochemical reduction reactions. Here, based on in situ spectroscopic and morphological evidence, we demonstrate the formation of a bridge CO* species through the adsorption-induced restructuring of a defect-rich Cu surface and its reactivity toward C-O bond dissociation and C-C coupling under hydrogenation reaction conditions. In corroboration with computational simulations, we attribute the unexpected reactivity to its enhanced adsorption strength and polarity with respect to commonly observed on-top CO* species. Our findings provide new insights into the strong correlation between the surface defect density and the selectivity toward methane, C₂ hydrocarbons, and oxygenates over Cu-based catalysts. The marked impact on reactivity highlights the crucial role of dynamic surface restructuring in determining the reaction selectivity over copper-based catalysts.

Understanding the electrical double layer (EDL) is fundamental for enhancing the efficiency, capacity, and stability of electrochemical systems. The EDL at the electrode/polyelectrolyte interface exhibits significantly different properties with a more complex structure compared to liquid electrolyte systems. Characterizing this intricate interface experimentally remains a major challenge. In this study, we directly observed the potential distribution at the electrode-polyelectrolyte interface using a delicate in situ electrochemical cell coupled with ambient pressure X-ray photoelectron spectroscopy (APXPS) at various probing depths. The electrode/polyelectrolyte (graphite/Nafion) interface was successfully constructed, and the APXPS measurements were performed under nonpolarizing conditions. The binding energy shift of the F 1s photoelectron with applied bias provided the information on potential distribution. Experimental results, simulated by the typical exponential and linear potential distribution models, indicate the formation of a 1-3 nm EDL at the electrode/polyelectrolyte interface. This work provides methodological guidance for in situ X-ray photoelectron spectroscopic studies and offers valuable fundamental data for electrochemical research.

The characterization of the electronic structure and chemical states at heterogeneous interfaces (e.g., gas–solid or liquid–solid) can be effectively achieved using ambient pressure x-ray photoelectron spectroscopy (AP-XPS). However, acquiring these properties under plasma conditions remains a significant challenge. In this study, we introduce an AP-XPS system equipped with a custom-built spatially confined plasma source. This configuration confines the plasma to a controlled region, with the plasma intensity precisely regulated by adjusting either the working distance or the applied voltage. This system enables the direct detection of plasma electrons and the real-time characterization of surface states during plasma–surface interactions. To validate its efficacy and versatility, we conducted two proof-of-concept experiments: argon (Ar) plasma etching of graphene and oxygen (O2) plasma oxidation of platinum (Pt). The results demonstrate that the Ar plasma effectively etches graphene, as evidenced by distinct changes in the XPS spectra. Similarly, the exposure of a Pt surface to the oxygen plasma induces pronounced surface oxidation. This system significantly extends the operando capabilities of AP-XPS for in situ studies of plasma-enhanced reactions. Its application holds considerable promise for advancing fundamental and applied research in materials science and chemical engineering, particularly in the areas of surface modification and catalytic processes.

Methanol synthesis through CO2 conversion (CO2 + 3H2 → CH3OH + H2O) offers a sustainable pathway for fuel production and chemical feedstock generation. Although Cu/ZnO/Al2O3 (CZA) catalysts are used industrially for methanol synthesis1, the valorization of CO2 is limited by the need to operate at elevated temperatures (500-550 K), and methanol selectivity is poor due to CO formation via the reverse water-gas shift (RWGS) reaction2,3. Here, we report a methanol production with 100% selectivity and a turnover frequency (TOF) of 1.17 molecules site-1 s-1 at 473 K on CuZn alloys by controlling the amount of water in CO2 and H2 mixture. Using scanning probe microscopy (SPM) from ultrahigh vacuum (UHV) to 5 bar pressure conditions and density functional theory (DFT) calculations, we directly visualize the mobile Zn3(OH)3 complexes generated by the synergistic interaction with H2O/H2 mixtures and demonstrated their structural flexibility in response to reaction intermediates. The synergy between Cu and Zn sites at the interface ensures complete CO2 conversion to methanol. Our study demonstrates the critical effect of precisely controlling the reaction environment for stabilizing highly active catalytic sites that would otherwise be thermodynamically unfavorable, offering a new strategy for catalyst design beyond traditional approaches of tuning surfaces and interfaces.