Thermodynamic phase control of Cu-Sn alloy electrocatalysts for selective CO2 reduction

In the electrochemical CO2 reduction reaction (CO2RR), Cu alloy electrocatalysts can control the CO2RR selectivity by modulating the intermediate binding energy. Here, we report the thermodynamic-based Cu-Sn bimetallic phase control in heterogeneous catalysts for selective CO2 conversion. Starting from the thermodynamic understanding about Cu-Sn bimetallic compounds, we established the specific processing window for Cu-Sn bimetallic phase control. To modulate the Cu-Sn bimetallic phases, we controlled the oxygen partial pressure (pO2) during the calcination of electrospun Cu and Sn ions-incorporated nanofibers (NFs). This resulted in the formation of CuO-SnO2 NFs (full oxidation), Cu-SnO2 NFs (selective reduction), Cu3Sn/CNFs, Cu41Sn11/CNFs, and Cu6Sn5/CNFs (full reduction). In the CO2RR, CuO-SnO2 NFs exhibited formate (HCOO-) production and Cu-SnO2 NFs showed carbon monoxide (CO) production with the faradaic efficiency (FE) of 65.3% at -0.99 V (vs. RHE) and 59.1% at -0.89 V (vs. RHE) respectively. Cu-rich Cu41Sn11/CNFs and Cu3Sn/CNFs enhanced the methane (CH4) production with the FE of 39.1% at -1.36 V (vs. RHE) and 34.7% at -1.50 V (vs. RHE). However, Sn-rich Cu6Sn5/CNFs produced HCOO- with the FE of 58.6% at -2.31 V (vs. RHE). This study suggests the methodology for bimetallic catalyst design and steering the CO2RR pathway by controlling the active sites of Cu-Sn alloys.

Rational design of stable Cu and AuCu nanoparticles for investigations of size-enhanced SERS applications

BACKGROUND

While significant progress has been made to clarify the effects of Au and Ag nanoparticle size on SERS enhancement, research on the size effects of copper nanoparticles and copper-related nanoalloys on SERS enhancement remain scarce. Nanoscale copper (Cu) is important because of its unique sensing and catalytic properties; however, research on its size and compositional effects remains a significant challenge because of the intricate fabrication process and difficulty in preventing oxidation.

RESULTS

Our study elucidated the size-dependent, surface-enhanced Raman scattering (SERS) of Cu NPs, particularly the sensing capabilities of both electromagnetic (EM) SERS at 1.5 × 103 and chemical enhancement (CE) SERS at 3.6 × 104 of approximately 58 nm Cu NPs. Additionally, a solution aging examination revealed preservation of the metal-related core structure, surface plasmon resonance, and SERS features of the PSMA/ONPG-coated Cu NPs for up to 7 days. With the introduction of galvanic replacement reactions and laser ablation syntheses, the incorporation of Au atoms enabled the fabrication of 7-75 nm AuxCuy nanoparticles by using the remaining Cu core after aging in water, which offered precise control over the Cu/Au ratio from 5/95 to 29/71. SERS measurements of the large AuxCuy nanoparticles amplified up to 1.4 × 104 of the EM-mediated vibrational signals from the adsorbed molecules. The strong Au-S chemical bonds of the Au-rich AuxCuy nanocrystals increased the CE SERS to 5.5 × 104, whereas the Au3Cu1 crystals at the AuxCuy interface decreased the CE SERS but improved the electron transfer for catalysis via SERS detection.

SIGNIFICANCE

Our research provides further insight into the structural and size effects of Cu and AuCu alloys used as SERS enhancers and offers avenues for designing cutting-edge SERS catalytic sensors tailored to Cu-related catalytic reactive structures. For the first time, we also manipulated the Cu atomic structure and surface composition to understand the significance of surface effects on SERS substrates of the Cu series from a nanoscale analytical perspective.

Strategies for overcoming challenges in selective electrochemical CO2 conversion to ethanol

The electrochemical conversion of carbon dioxide (CO2) to valuable chemicals is gaining significant attention as a pragmatic solution for achieving carbon neutrality and storing renewable energy in a usable form. Recent research increasingly focuses on designing electrocatalysts that specifically convert CO2 into ethanol, a desirable product due to its high-energy density, ease of storage, and portability. However, achieving high-efficiency ethanol production remains a challenge compared to ethylene (a competing product with a similar electron configuration). Existing electrocatalytic systems often suffer from limitations such as low energy efficiency, poor stability, and inadequate selectivity toward ethanol. Inspired by recent progress in the field, this review explores fundamental principles and material advancements in CO2 electroreduction, emphasizing strategies for ethanol production over ethylene. We discuss electrocatalyst design, reaction mechanisms, challenges, and future research directions. These advancements aim to bridge the gap between current research and industrialized applications of this technology.

Phase control of solid-solution RuIn nanoparticles and their catalytic properties

The properties of solids could be largely affected by their crystal structures. We achieved, for the first time, the phase control of solid-solution RuIn nanoparticles (NPs) from face-centred cubic (fcc) to hexagonal close-packed (hcp) crystal structures by hydrogen heat treatment. The effect of the crystal structure of RuIn alloy NPs on the catalytic performance in the hydrogen evolution reaction (HER) was also investigated. In the hcp RuIn NPs, enhanced HER catalytic performance was observed compared to the fcc RuIn NPs and monometallic Ru NPs. The intrinsic electronic structures of the NPs were investigated by valence-band X-ray photoelectron spectroscopy (VB-XPS). The d-band centre of hcp RuIn NPs obtained from VB-XPS was deeper than that of fcc RuIn NPs and monometallic Ru NPs, which is considered to enable the hcp RuIn NPs to exhibit enhanced HER catalytic performance.

Efficient catalyst screening using graph neural networks to predict strain effects on adsorption energy

Small-molecule adsorption energies correlate with energy barriers of catalyzed intermediate reaction steps, determining the dominant microkinetic mechanism. Straining the catalyst can alter adsorption energies and break scaling relationships that inhibit reaction engineering, but identifying desirable strain patterns using density functional theory is intractable because of the high-dimensional search space. We train a graph neural network to predict the adsorption energy response of a catalyst/adsorbate system under a proposed surface strain pattern. The training data are generated by randomly straining and relaxing Cu-based binary alloy catalyst complexes taken from the Open Catalyst Project. The trained model successfully predicts the adsorption energy response for 85% of strains in unseen test data, outperforming ensemble linear baselines. Using ammonia synthesis as an example, we identify Cu-S alloy catalysts as promising candidates for strain engineering. Our approach can locate strain patterns that break adsorption energy scaling relations to improve catalyst performance.

Silver-Copper Alloy Nanoinks for Ambient Temperature Sintering

There is an increasing need to reduce the silver content in silver-based inks or pastes and achieve low-temperature sintering for scalable and low-cost production of printed wearable electronics. This need depends on the ability to control the metal composition and the surface properties of the nanoinks. Alloying silver with copper provides a pathway for meeting the need in terms of cost reduction, but little is known about the composition controllability and the low-temperature sintering capability. We report herein a scalable wet chemical synthesis of bimetallic silver-copper alloy nanoinks with room temperature sintering properties. The bimetallic alloy nanoparticles with a controllable composition can be formulated as stable nanoinks. The nanoinks printed on paper substrates are shown to sinter under room temperature. In addition to composition dependence, the results reveal an intriguing dependence of sintering on humidity above the printed nanoink films. These findings are assessed based on theoretical simulation of the sintering processes via surface-mediated sintering and interparticle necking mechanisms in terms of nanoscale adsorption, adhesion and diffusion, and surface free energies. Implications of the findings for room temperature fabrication of wearable sensors are also discussed.

Synergistic effect of Cu/Cu2O surfaces and interfaces for boosting electrosynthesis of ethylene from CO2 in a Zn–CO2 battery

We constructed Cu/Cu2O hybrid catalysts with highly active surfaces/interfaces to realize a synergistic effect, thus improving the selectivity and efficiency of C2H4 production.