Alexander J. Cowan

High‐entropy‐alloy (HEA) nanocrystals offer tremendous potential as next‐generation catalysts for complex electrochemical reactions. Nonetheless, there is a relative dearth of attention regarding the structural evolution of HEAs under electrochemical conditions. We herein used platinum‐group HEA nanocubes, initially enclosed by well‐defined {100} facets, as electrocatalysts for the multistep ethanol oxidation reaction (EOR). Notably, the prepared catalysts demonstrate an 8.3‐fold enhancement in specific activity during electrochemical cycling, driven by the structural evolution of catalyst facets. This transformation leads to a severely beveled cubic morphology characterized by an approximately equal distribution of {100}, {110}, and {111} facets, while preserving the compositional homogeneity and high‐entropy nature, as confirmed by high‐resolution transmission electron microscopy and synchrotron‐based x‐ray absorption spectroscopy. In situ surface‐enhanced infrared absorption spectroscopy, electrochemical stripping experiments, and computational calculations reveal that the enhanced performance originates from improved C─C bond cleavage and superior resistance to poisoning by formate intermediates (HCOO _ad ). These features promote complete oxidation of ethanol to CO ₂ , a critical step for maximizing efficiency in direct alcohol fuel cells for renewable energy applications.

High‐entropy‐alloy (HEA) nanocrystals offer tremendous potential as next‐generation catalysts for complex electrochemical reactions. Nonetheless, there is a relative dearth of attention regarding the structural evolution of HEAs under electrochemical conditions. We herein used platinum‐group HEA nanocubes, initially enclosed by well‐defined {100} facets, as electrocatalysts for the multistep ethanol oxidation reaction (EOR). Notably, the prepared catalysts demonstrate an 8.3‐fold enhancement in specific activity during electrochemical cycling, driven by the structural evolution of catalyst facets. This transformation leads to a severely beveled cubic morphology characterized by an approximately equal distribution of {100}, {110}, and {111} facets, while preserving the compositional homogeneity and high‐entropy nature, as confirmed by high‐resolution transmission electron microscopy and synchrotron‐based x‐ray absorption spectroscopy. In situ surface‐enhanced infrared absorption spectroscopy, electrochemical stripping experiments, and computational calculations reveal that the enhanced performance originates from improved C─C bond cleavage and superior resistance to poisoning by formate intermediates (HCOO _ad ). These features promote complete oxidation of ethanol to CO ₂ , a critical step for maximizing efficiency in direct alcohol fuel cells for renewable energy applications.

High-entropy-alloy (HEA) nanoparticles containing at least five elements are an emerging family of catalysts. Due to the increased complexity of multicomponent atomic mixing, the size reduction of HEA nanoparticles down to around 1 nm is a substantial challenge, which is crucial to enhance the efficiency of atom utilization. Herein, we report a template-confined synthesis strategy for constructing a library of ultrasmall HEA nanoparticles with sizes of approximately 1 nm and compositions containing up to ten elements, including Pt, Pd, Ru, Rh, Fe, Co, Ni, Cu, Mo, and Zn. By leveraging the confinement effect of the mesoporous carbon structure and the autocatalytic reduction of the metal-precursor mixture at a low reaction temperature, we successfully achieve the uniform embedding of a diverse array of ultrasmall multicomponent HEA nanoparticles within the mesoporous framework. Additionally, we demonstrate that the 1 nm PtRuFeCoNi nanoparticles exhibit enhanced mass activity and superior atom utilization in both hydrogen evolution and hydrogen oxidation reactions, surpassing other quinary HEA and commercial Pt/C catalysts. Furthermore, operando X-ray absorption spectroscopy and theoretical calculations suggest a cooperative multielement effect among the five constituent elements, in which Pt- and Ru-containing local environments provide favorable sites for H-intermediate adsorption and contribute to the enhanced catalytic performance.

Consistent and reproducible synthesis of SiO₂-coated Au nanoparticles, which are widely used as shell-isolated nanoparticles for enhanced Raman spectroscopy (SHINERS), is limited by the lack of rapid, routine methods to determine shell thickness and aggregation state. Here, differential centrifugal sedimentation (DCS) is demonstrated as a benchtop, collective-averaged technique capable of evaluating Au–SiO₂ nanoparticles for SHINERS on time scales of under 10 min. Shell thicknesses determined by DCS show close agreement with transmission electron microscopy (TEM) images within the critical 3.5–5.5 nm range governing reliable pinhole free Raman enhancement, while simultaneously revealing early stage aggregation beyond the reach of UV–visible spectroscopy. By converting shell thickness and aggregation assessment into a rapid, decision-ready measurement, DCS enables routine quality control and synthesis-level optimization of reproducible particles for use in SHINERS.

Catalysts achieve changes in the rate through modification of the free energy of adsorbed intermediates and transition states (TrS). Binding energies of intermediates and TrS are strongly correlated, and modifications in catalyst composition are often ineffective in breaking these correlations, leading to minimal change in rate. Such scaling relationships are reported throughout catalysis. The surface spin state of a magnetic metal can change adsorption energies, offering a way to overcome scaling relationships. However, experimentally, this approach appears reliant on the use of ferromagnetic materials, limiting applicability. Here, we show that tunable changes in electrocatalytic activity for the hydrogen evolution reaction (HER) can be achieved at (originally) nonmagnetic metals (Au and Pt) through the use of a multilayer electrode structure that contains a ferromagnetic alloy (CoB) beneath a thin (5-20 nm) film of Pt or Au. Analysis of the dependence of the catalytic current on the thickness of the Au or Pt capping layer and on the direction of the stray magnetic field allows us to rule out the presence of magnetohydrodynamic effects. Instead, we conclude that transfer of ferromagnetism from the ferromagnet to the Au or Pt takes place through proximity-induced magnetism (PIM) via exchange interactions and/or a spin polarized current. Density Functional Theory simulations trace changes in the breaking of the scaling relationship for the Tafel HER mechanism. Overall, our experiments show that thin-film electrodes, based on routine structures from the spintronics community, are a potentially versatile platform for achieving spin-polarized catalysis at originally nonmagnetic metals.

A common strategy to improve the efficiency of organic photocatalysts for hydrogen production from aqueous mixtures is to create bulk heterojunction nanoparticles comprised of intermixed donor and acceptor phases that allow for efficient charge separation after photoexcitation. However, many of these systems possess poor stability due to aggregation of these nanoparticles under operating conditions. Moreover, the use of surfactants, that inhibit aggregation and promote donor–acceptor phase intermixing, can form an insulating barrier that reduces the photocatalytic efficiency of these nanoparticles. Here, these issues are bypassed by preparing a single‐component organic heterojunction‐type polymer, P40 , in which a molecular donor, pyrene, is tethered to poly(fluorene‐ co ‐dibenzo[ b , d ]thiophene sulfone), a conjugated polymer acceptor. By tethering the donor and acceptor together, phase intermixing is guaranteed without the need for costly post‐synthesis processing or insulating surfactants. Moreover, the influence of pyrene in P40 is determined to be multifaceted, as it influences the dynamics of the excited state, the aggregate microstructure, and the local solvent environment. P40 is found to have an exceptional external quantum efficiency of 38% at 420 nm in the presence of triethylamine as a hole scavenger, the highest value reported for any linear conjugated polymer to date for sacrificial hydrogen production.

‘Through-electrode’ vibrational sum frequency generation elucidates the interface structure of CH ₃ CN in the electric double layer. Changes to micro-environments are observed in the presence of H ₂ O and N -methyl-2-pyrrolidone additives.

We report herein the synthesis, spectroscopic and electrochemical characterization, as well as electrocatalytic properties toward heterogeneous electrochemical CO₂ reduction of two mononuclear copper(II) complexes, namely, [Cu(L)]²⁺ (1) and [Cu(QTPy)]²⁺ (2), where L = 8-([2,2'-bipyridin]-6-yl)-2-(pyridin-2-yl)quinoline and QTPy = 2,2':6',2″:6″,2‴-quaterpyridine. The two complexes 1 and 2 have been first successfully immobilized onto multiwalled carbon nanotubes (MWCNTs) grafted on glassy carbon electrodes, as shown by X-ray photoelectron spectroscopy and cyclic voltammetry. Electroreduction of carbon dioxide by the grafted complexes has been investigated in an aqueous KHCO₃ medium at neutral pH. Comparative studies highlight the better catalytic performance of the complex bearing L rather than QTPy under the same experimental conditions. Controlled potential electrolysis (CPE) at low overpotential (-0.55 V vs reversible hydrogen electrode (RHE)) displays high selectivity for carbon monoxide production with complex 1 (Faradaic efficiency (FE_CO = 75%)). Furthermore, in situ and ex-situ analyses of the electrolysis evidence no modification of the immobilized mononuclear complex upon CPE, which is rare for grafted copper systems as well as no leach of copper in the electrolyte solution. Noteworthy, the implementation of the complexes into zero-gap electrolyzers allows the strong enhancement of FE_CO for complex 1, reaching 100% at -0.60 V vs RHE, whereas complex 2 remains poorly selective, hence clearly highlighting the strong impact of the ligand topology on the catalytic properties of the complexes.

We report herein the synthesis, spectroscopic and electrochemical characterization as well as electrocatalytic properties toward heterogeneous electrochemical CO2 reduction of two mononuclear copper(II) complexes, namely [Cu(L)]2+ (1) and [Cu(QTPy)]2+ (2) where L = 8-([2,2'-bipyridin]-6-yl)-2-(pyridin-2-yl)quinoline and QTPy = 2,2':6',2'':6'',2'''-quaterpyridine. The two complexes 1 and 2 have been first successfully immobilized onto multiwalled carbon nanotubes (MWCNTs) glassy carbon electrodes as shown by X-ray photoelectron spectroscopy and cyclic voltammetry. Electroreduction of carbon dioxide by the grafted complexes has been investigated in aqueous KHCO3 medium at neutral pH. Comparative studies highlight the better catalytic performance of the complex bearing L rather than QTPy under the same experimental conditions. Controlled potential electrolysis (CPE) at low overpotential (–0.55 V vs RHE) displays high selectivity for carbon monoxide production with complex 1 (Faradaic Efficiency (FECO = 75%)). Furthermore, in-situ and ex-situ analyses of the electrolysis evidence no modification of the immobilized mononuclear complex upon CPE which is rare for grafted copper systems, as well as no leach of copper in the electrolyte solution. Noteworthy, implementation of the complexes into zero-gap electrolysers allows the strong enhancement of FECO for complex 1, reaching 100% at –0.60 V vs RHE, whereas complex 2 remains poorly selective, hence clearly highlighting the strong impact of the ligand topology on the catalytic properties of the complexes.

Bipolar membranes (BPM), composed of a cation exchange layer and an anion exchange layer, can enable steady-state operation at different pHs at the cathode and anode in a water electrolyzer. This allows optimizing the cathode and anode catalysts for acidic and alkaline environments, respectively, which increases the scope for low-cost materials. Commercially available BPMs are operational only in a limited current range, therefore we aimed to develop custom BPMs for higher currents that are easily fabricated, mechanically stable, and suitable for storage in dry form. We used commercial single membranes combined with TiO2 as the water dissociation catalyst in the junction, and found that spin-coating of TiO2 yielded reproduceable interfaces for water dissociation. Electrochemical Impedance Spectroscopy (EIS) was used to deconvolute the water dissociation resistance from other processes, leading to better understanding of the parameters that determine BPM performance. Hot-pressing of the BPM led to stronger adhesion of the two membrane layers, creating a durable self-standing BPM. Using this workflow, future high-performance BPMs can be developed and investigated, for use not only in water electrolyzers but also CO2 electrolyzers where BPMs are required for higher CO2 utilization efficiency.