Electrochemical CO2 reduction provides a promising strategy to synthesize C2+ compounds with reduced carbon intensity; however, high overall energy consumption restricts practical implementation. Using acidic media enables high CO2 utilization and low liquid product crossover, but to date has suffered low C2+ product selectivity. Here we hypothesize that adjacent pairs of atomic-copper active sites may favour C–C coupling, thus facilitating C2+ product formation. We construct tandem electrocatalysts with two distinct classes of active sites, the first for CO2 to CO, and the second, a dual-atomic-site catalyst, for CO to C2+. This leads to an ethanol Faradaic efficiency of 46% and a C2+ product Faradaic efficiency of 91% at 150 mA cm−2 in an acidic CO2 reduction reaction. We document a CO2 single-pass utilization of 78% and an energy efficiency of 30% towards C2+ products; an ethanol crossover rate of 5%; and an ethanol product concentration of 4.5%, resulting in an exceptionally low projected energy cost of 249 GJ t−1 for the electrosynthesis of ethanol via the CO2 reduction reaction. (Figure presented.)

Zinc oxide (ZnO) is a semiconductor with a wide range of applications, and often the properties are modified by metal-ion doping. The distribution of dopant atoms within the ZnO crystal strongly affects the optical and magnetic properties, making it crucial to comprehend the structure down to the atomic level. Our study reveals the dopant structure and its contents in Eu-doped ZnO nanosponges with up to 20% Eu-O clusters. Eu was distributed over the ZnO:Eu crystals, with an additional amorphous intercrystalline phase observed, especially in the 20% Eu sample. The electron pair distribution function revealed the presence of nonperiodic Eu3+-oxide clusters and proved highly effective for analyzing the coordination environment of Eu-O, ranging from 2.0 to 2.8 A. It uncovered three-, four-, and five-coordinate Eu-O configurations in the 20% Eu sample, and there were significant changes in Eu coordination between the samples, which is ascribed due to the intercrystalline phase. The proposed method offers a potential characterization routine for a detailed investigation of complex doped materials.

The electrocatalytic approach of combining N2 and H2O to produce ammonia, known as the electrocatalytic N2 reduction reaction (eNRR), has garnered significant attention due to its environmental benefits and potential for supporting a decentralized agricultural economy. However, the underlying chemistry governing the reaction pathways remains poorly understood, hindering the design of low-cost and efficient eNRR catalysts. Here we report the enhancement of the electrocatalytic eNRR activity of perovskite oxides by tuning the reaction pathway through a “donation-back-donation” mechanism. This is achieved by controlling the spin state via adjusting the distribution of d orbital electrons in low-cost transition metals, such as cobalt. Specifically, the cobalt in perovskite SrCoO3 (SC) with a low-spin state demonstrates an 18 times higher ammonia yield rate compared to that in Co3O4 and 1.5 times higher than cobalt in perovskite LaCoO3 (LC). The low spin states of cobalt in SC enable better control of the eNRR reaction pathway over the transformation of *N2H to *NHNH or *NNH2, resulting in alternating hydrogenation in SC rather than distal hydrogenation in LC with a high spin state. The unprecedented improvement in eNRR by regulating the spin state of Co demonstrates the bright of low-cost Co-based electrocatalysts for ammonia production.

The pair distribution function (PDF) is a powerful tool for structure analysis. It maps atom-pair correlations of an entire observed region into real space.  Contributed by the strong interaction between electrons and matter, and the tuneable electron beam size in transmission electron microscope (TEM), this concept can be adapted to TEM to produce an electron‑based PDF (ePDF), which enables local structure analysis at the nanoscale. Moreover, by extending one‑dimensional powder PDF into two and three dimensions, multi‑dimensional ePDF provides in‑lab tools for probing 3D atom-atom pair correlation within nanocrystals. In this thesis, I present the development and application of multi‑dimensional ePDF methods across a variety of nanomaterials.

In the initial study, powder ePDF was applied to Eu‑doped ZnO nanosponges. High‑resolution scanning transmission electron microscopy (STEM) imaging revealed Eu incorporation both doped within the hexagonal ZnO lattice, and as Eu‑rich amorphous phase at grain boundaries. Subsequent ePDF analysis quantified different Eu-O coordination environments, establishing a theoretical and practical foundation to understand the structure of Eu-doped ZnO nanosponges.

To obtain angular‑resolved atom-pair correlations in single crystal specimens, this thesis adapts both the three‑dimensional PDF (3D‑PDF) and its difference counterpart (3D-ΔPDF) to TEM. A customized data processing pipeline then enables in‑lab computation of full 3D-ePDFs. To demonstrate the method’s versatility, we first applied 3D-ePDF to piezoceramic perovskites, where it cleanly resolved both in‑phase and antiphase octahedral tilts and quantitatively measured A‑site cation displacements. Next, we turned to a novel structural material, high‑entropy alloys (HEAs). STEM imaging initially revealed an uneven distribution of heavy elements, and subsequent 3D-ΔPDF analysis uncovered local chemical ordering networks within structure. In particular, we showed that Hf atoms preferentially occupy specific lattice sites. Such finding correlates directly with the alloy’s enhanced ductility and strength.

Finally, the beam‑sensitive Prussian blue analogues (PBAs) were studied. Considering the PBAs degraded fast under electron beam illumination, the serial electron diffraction (SerialED) with 2D ePDF was applied. We successfully identifying correlated vacancy networks and local disorder that conventional TEM could not capture due to radiation damage.

Overall, our work establishes a suite of complementary ePDF methodologies, 1D, 2D, and 3D, tailored to sample stability and complexity. By harnessing the strong electron-matter interaction and accessible in‑lab instrumentation, these approaches deliver unprecedented local‑structure insights across crystalline, amorphous, and composite materials, paving the way for rational design of next‑generation functional materials.

We present the successful synthesis and characterization of a one-dimensional high-entropy oxide (1D-HEO) exhibiting nanoribbon morphology. These 1D-HEO nanoribbons exhibit high structural stability at elevated temperatures (to 1000°C), elevated pressures (to 12 gigapascals), and long exposure to harsh acid or base chemical environments. Moreover, they exhibit notable mechanical properties, with an excellent modulus of resilience reaching 40 megajoules per cubic meter. High-pressure experiments reveal an intriguing transformation of the 1D-HEO nanoribbons from orthorhombic to cubic structures at 15 gigapascals followed by the formation of fully amorphous HEOs above 30 gigapascals, which are recoverable to ambient conditions. These transformations introduce additional entropy (structural disorder) besides configurational entropy. This finding offers a way to create low-dimensional, resilient, and high-entropy materials.

When electrocatalysts are prepared, modification of the morphology is a common strategy to enhance their electrocatalytic performance. In this work, we have examined and characterized nanorods (3D) and nanosheets (2D) of nickel molybdate hydrates, which previously have been treated as the same material with just a variation in morphology. We thoroughly investigated the materials and report that they contain fundamentally different compounds with different crystal structures, chemical compositions, and chemical stabilities. The 3D nanorod structure exhibits the chemical formula NiMoO4<middle dot>0.6H(2)O and crystallizes in a triclinic system, whereas the 2D nanosheet structures can be rationalized with Ni3MoO5-0.5x(OH)(x)<middle dot>(2.3 - 0.5x)H2O, with a mixed valence of both Ni and Mo, which enables a layered crystal structure. The difference in structure and composition is supported by X-ray photoelectron spectroscopy, ion beam analysis, thermogravimetric analysis, X-ray diffraction, electron diffraction, infrared spectroscopy, Raman spectroscopy, and magnetic measurements. The previously proposed crystal structure for the nickel molybdate hydrate nanorods from the literature needs to be reconsidered and is here refined by ab initio molecular dynamics on a quantum mechanical level using density functional theory calculations to reproduce the experimental findings. Because the material is frequently studied as an electrocatalyst or catalyst precursor and both structures can appear in the same synthesis, a clear distinction between the two compounds is necessary to assess the underlying structure-to-function relationship and targeted electrocatalytic properties.

The acidic oxygen evolution reaction (OER) is essential for many renewable energy conversion and storage technologies. However, the high energy required to break the strong covalent O-H bond of H₂O in acidic media results in sluggish OER kinetics. Here, we report the critical role of iron in a new family of iron-containing yttrium ruthenate (Y_2-xFe_xRu₂O_7-δ) electrocatalysts in highly increasing the electrophilicity of surface oxygen, leading to a significant reduction of the kinetics barrier by 33%, thus an exceptional OER mass activity of 1,021 A· up to 12.4 and 7.7 times that of Y₂Ru₂O_7-δ and RuO₂, respectively. Introducing iron reduces the Mulliken atomic charge on the O sites in the generated Ru-O-Fe structure, thereby facilitating the acid-base nucleophilic assault from H₂O and reducing the free energy on the rate-determining step of OER. This work provides an effective strategy to reduce the kinetics barrier to achieve highly efficient and economic OER in acidic conditions.

Understanding the reconstruction of surface sites is crucial for gaining insights into the true active sites and catalytic mechanisms. While extensive research has been conducted on reconstruction behaviors of atomically dispersed metallic catalytic sites, limited attention has been paid to non-metallic ones despite their potential catalytic activity comparable or even superior to their noble-metal counterpart. Herein, we report a carbonaceous, atomically dispersed non-metallic selenium catalyst that displayed exceptional catalytic activity in the hydrazine oxidation reaction (HzOR) in alkaline media, outperforming the noble-metal Pt catalysts. In situ X-ray absorption spectroscopy (XAS) and Fourier transform infrared spectroscopy revealed that the pristine SeC₄ site pre-adsorbs an ∗OH ligand, followed by HzOR occurring on the other side of the OH–SeC₄. Theoretical calculations proposed that the pre-adsorbed ∗OH group pulls electrons from the Se site, resulting in a more positively charged Se and a higher polarity of Se–C bonds, thereby enhancing surface reactivity toward HzO/R.

The development of electrocatalysts for the oxygen evolution reaction (OER) especially in acidic media remains the major challenge that still requires significant advances, both in material design and mechanistic exploration. In this study, the incorporation of cobalt in Y_2-xCo_xRu₂O_7−δ results in an ultrahigh OER activity because of the charge redistribution at e_g orbitals between Ru and Co atoms. The Y1.₇₅Co_0.25Ru₂O_7−δ electrocatalyst exhibits an extremely small overpotential of 275 mV in 0.5 m H₂SO₄ at the current density of 10 mA cm⁻², which is smaller than that of parent Y₂Ru₂O_7−δ (360 mV) and commercial RuO₂ (286 mV) catalysts. The systematic investigation of the composition related to OER activity shows that the Co substitution will also bring other effective changes, such as reducing the bandgap, and creating oxygen vacancies, which result in fast OER charge transfer. Meanwhile, the strengthening of the bond hybridization between the d orbitals of metal (Y and Ru) and the 2p orbitals of O will intrinsically enhance the chemical stability. Finally, theoretical calculations indicate that cobalt substitution reduces the theoretical overpotential both through an adsorbate evolution mechanism and a lattice oxygen-mediated mechanism.

The complicated electrochemical catalytic conversion process of polysulfides in metal–sulfur batteries involves three steps: adsorption, catalysis, and desorption process. Even as huge efforts are made for the understanding of the separate steps (especially for the adsorption and catalysis process), research focusing on the entire process is still scarce. Herein, a series of cobalt phosphides (CoP, CoP₂, and CoP₃) is employed with identical hollow morphology as model electrocatalysts to investigate the significance of the desorption process and discuss the balancing among the adsorption, catalysis, and desorption of lithium polysulfides (LiPSs). The experimental data demonstrate that, compared to CoP and CoP₃, CoP₂ exhibits moderate adsorption of LiPSs, which enhances the reduction kinetics of S₈ to Li₂S and regulates the desorption of short-chain LiPSs. Theoretical calculations further confirm that CoP₂ with moderate adsorption of LiPSs exhibits better redox kinetics of LiPSs compared to CoP and CoP₃. Moderate adsorption enables the CoP₂-based sulfur cathode to deliver excellent stability with 86% capacity retention (2.6 and 2.0 times higher than CoP and CoP₃, respectively) over 1000 cycles at 1 C. All these results indicate that in the adsorption-catalysis-desorption chain for LiPSs, all steps need to be considered rather than just focusing on one step of the process.