87 Search Results

The electrochemical CO₂ reduction (eCO₂R) offers a compelling route for converting CO₂ into value-added fuels and chemicals. Among CO₂-derived products, methane (CH₄) occupies a distinct position, serving both as a key intermediate for emerging cascade electro-oxidation to oxygenates and as a strategically important extraterrestrial fuel that can be generated in situ from off-planet CO₂ resources. Although Cu-based catalysts capable of selectively producing CH₄ have been reported, they seldom sustain high selectivity at practically relevant current densities. Here, we created a single-step co-pyrolysis strategy toward generating and anchoring Cu sub-nanometer clusters (Cu_SNC) atop Cu-N_x single-atom (SA) motifs embedded within N-doped carbonmore » (NC), with controllable nanostructures through tuning of the synthesis parameters. Complementary spectroscopic analyses and density functional theory (DFT) calculations help reveal a structure−activity correlation that could guide the catalyst design. The Cu_SNC@NC sample synthesized at 550 °C pyrolysis temperature (best described and modeled as Cu₃-CuN₄ domains) represents the most effective combination of cluster size, metal-nitrogen coordination, and adsorption energetics needed to selectively promote CH₄ generation versus other eCO₂R products. Incorporating pulsed electrolysis and hydrophobicity-modulated transport tuning at the triple-phase boundary (TPB) further enhanced CH₄ production achieving a partial CH₄ current density of ∼321 mA cm⁻², 53% Faradaic efficiency (FECH₄), and less than 4% combined FE for other eCO₂R products, simplifying downstream CH₄ purification or upgrading. This work establishes generalizable principles for controlling Cu cluster atomicity and metal−nitrogen coordination, both of which are recognized determinants of CH₄-efficient eCO₂R.« less

Driven by environmental and health concerns related to per- and polyfluoroalkyl substances (PFAS), there has been growing interest in developing fluorine-free proton (H⁺) exchange membrane (PEM) materials for fuel cells and water electrolyzers. In this study, we present a side-by-side comparison of the key transport properties of submicron thick, PFAS-free amorphous silicon dioxide (SiO₂) membranes to Nafion, a fluorinated polymer electrolyte membrane that represents the industry standard for PEM fuel cells and electrolyzers. Here, measurements of proton (H⁺) conductivity (σ_H⁺), hydrogen (H₂) permeability (P_H2), and electrical resistivity (ρ_e^–) were conducted using model thin films comprised of SiO₂ membranes deposited bymore » atomic layer deposition (ALD). Although the H⁺ conductivity of the SiO₂ membranes is 2–3 orders of magnitude lower than Nafion, the addition of phosphorus dopants (PO_x) improves H⁺ conductivity such that the area specific membrane resistance of thin (<50 nm) PO_x-doped SiO₂ membranes is more than an order of magnitude lower than Nafion-117. Importantly, the safe operation of such nanoscale membranes within a PEM electrolyzer is feasible thanks to the low H₂ permeability of dense SiO₂-based membranes, which are predicted to limit H₂ crossover rates to acceptable levels for pressures up to ≈ 100 bar. As a proof-of-principle demonstration, a chip-scale water electrolyzer based on 100 nm thick PO_x-SiO₂ membrane is shown to achieve a current density of 2 A cm^–2 at a potential of 2.5 V. If this technology can be successfully scaled up, H⁺ conducting oxide membranes offer an attractive PFAS-free alternative to Nafion for efficient and durable water electrolysis and fuel cell technologies.« less

High-entropy alloys (HEAs) provide uniquely tunable structural and electronic properties that enable robust electrocatalysis. While compositional manipulation of HEAs is well-known, systematically controlling the crystalline phase and morphology remains a challenge that could provide new avenues for controlling reactive sites and physical properties. Here, we show the preferential stabilization of mixed fcc/bcc to fcc phases by controlling the Au content in quinary AuPdFeCoNi HEA nanoparticles. This systematic structural and compositional control, when investigated with an ensemble of electronic, X-ray synchrotron, and surface techniques, allows us to identify the critical short- (few-Å) and medium- (6–10 Å) range structural motifs that delivermore » exceptional hydrogen evolution reaction (HER) catalysis. Specifically, these HEAs exhibit both outstanding durability (240 h) and high mass activity (50 A/mg_PGM) normalized to noble metal content, outperforming commercial Pt/C (3.18 A/mg_PGM). This structural control over HEA morphology, and its direct association with changes in specific metallic oxidation states and pair–pair atomic structural features, provides new means and strategies for finely designing robust and sustainable electrocatalysts with a majority nonprecious metal composition.« less

Herein, we introduce a straightforward synthesis approach for highly active dendritic multimetallic high-entropy alloy (DMHEA@PtIrPdAgRu) nanoparticles with sufficient entropic mixing, featuring uniform distribution of five noble group metals (Pt, Ir, Pd, Ag, and Ru) via a block copolymer-mediated one-pot solvothermal reduction method for oxygen evolution reaction (OER). In this synthesis, N,N-dimethylformamide (DMF) is used as a reductant as well as solvent and core–shell-corona-type (poly(styrene)-block-poly(vinylpyridine)-block-poly(ethylene oxide)) (PS-PVP-PEO) block copolymer as a structure directing agent. The cooperative effect between the copolymer architecture and the reducing environment of DMF promoted a confined nucleation mechanism for forming a single-phase dendritic structure HEA with highmore » compositional uniformity, thereby mitigating phase segregation, a common challenge in the synthesis of multimetallic nanoparticles. This prepared DMHEA@PtIrPdAgRu catalyst exhibits a low overpotential of 490 mV to attain a high current density of 100 mA cm^–2 with a Tafel slope of 442 mV dec^–1 for oxygen evolution. The superior OER performance is attributed to the synergistic cooperation among its active and coordinated metal centers as well as the incorporation of corrosion-resistant metal like platinum.« less

Efficiency of water splitting for hydrogen production is often limited by the sluggish kinetics of multiple electronic transfers required in the heterogeneous oxygen evolution reaction (OER). Catalyst design for reducing the high OER overpotential remains a major scientific challenge. Lattice-strain engineering, a method for tuning the electronic structure and surface geometric configuration of active sites, may greatly affect the interaction between adsorbates and catalytic surfaces for high activity and stability. Here, in this study, we present the synthesis of biphasic oxides of YPrSrRuMnO_x, which consists of distinct phases of Y₂Ru₂O₇ pyrochlore and (Pr_0.7Sr_0.3)MnO₃ perovskite, and the development of a suitablemore » analytical approach to study the strain–catalytic property relationship. Linear sweep voltammetry results reveal that the biphasic oxide exhibits approximately 3.1 times greater mass activity and 2.4 times larger turnover frequency (TOF) than single-phase Y₂Ru₂O₇ in the 0.1 M HClO₄ electrolyte. The biphasic catalyst is also about 3 times more stable than the single-phase oxide under acidic conditions. X-ray photoelectron spectroscopy, nitrogen isotherm, and electrochemical surface area analyses indicate that the oxidation state, specific surface area, and electrochemical surface area do not cause enough difference in the observed enhancement of OER performance. We examined the effects of microstrain on electrocatalysis, originating from lattice mismatch between different phases, using three different structural models. Specifically, we compared the Williamson–Hall method, standard stress–strain analysis, and Rietveld refinement in analyzing the structure–property relationship. Strain mapping using geometric phase analysis (GPA) further revealed significant microstrain and lattice dislocations localized near phase boundaries in the biphasic oxide, in contrast to the uniform strain in single-phase materials. The results reveal that the increased microstrain correlates well with the improved OER performance, as the biphasic oxide catalyst exhibits 2–3 times greater microstrain than Y₂Ru₂O₇ pyrochlore.« less

Electrolytic CO reduction was investigated at copper electrocatalysts in zero-gap membrane electrode assemblies as a function of buffering agents and cofeeding with CO₂ or Ar. Results show an acetate Faradaic efficiency (FE) of 90% at 300 mA cm⁻² using pure CO feeds and phosphate-buffered anolyte near pH 8. When using CO feeds with more alkaline anolytes, the hydrogen evolution reaction becomes the dominant reduction reaction, independent of the buffer. Product distributions of cofeeding experiments with CO and CO₂ show that increasing CO₂ cofeeding results in increased selectivity toward ethylene (42% FE) in near-neutral KHCO₃ anolytes or ethanol (40% FE) inmore » alkaline KOH anolytes. Evaluation of several commercial anion exchange membranes shows similar selectivity trends, suggesting product selectivity is dominated by the local pH and surface coverage of CO. Based on these results, we propose pH buffering and CO coverage behaviors that facilitate high selectivities to acetate.« less

Nickel oxide nanocubes with increased (100) surface facet presence (NiO(100)) were synthesized through a molten salt synthesis procedure to probe their oxygen evolution reaction (OER) activity in order to investigate the relationship between the surface facet and OER performance. While altering the synthesis parameters to decrease NiO(100) particle sizes and agglomeration, a polycrystalline NiO nanoparticle system formed from using Li2O as a Lux-Flood base (labelled Li2O-MSS NiO, where MSS stands for molten salt synthesis). This novel synthesis was further elaborated and the obtained materials were also tested for OER activity. After thorough structural characterization to determine crystallinity, lattice spacings, andmore » elemental distribution, their OER activity was compared versus high surface area NiO(111) nanosheets in a three-electrode rotating disk electrode (RDE) system. The activity trend of (111) > Li2O-MSS > (100) was observed. This decrease in activity of the nanocube and polycrystalline samples was explained by differences between theoretical and experimental conditions, differences in ink rheology and resulting catalyst layer properties, and significant agglomeration seen in the imaging of the sample. Methods for improving the OER activity of these samples are discussed in the conclusion of this study.« less

State-of-the-art OER (oxygen evolution reaction) catalyst syntheses require the use of expensive metals (i.e. Ir) with complex and time-consuming synthetic routes, difficulty in control, and impractical yields. Although some reported catalysts show improved performance (i.e. activity, stability, lowering Ir content with Ru), their synthesis is costly and not viable for scale-up. Here we demonstrate a practical, reliable, and scalable one-pot synthesis method for OER catalysts based on borohydride reduction to quickly yield >100 mg of Ir, Ru, and IrRu nanoparticles (1.6 ± 0.2 nm) with outstanding batch-to-batch consistency. Both mono- and bi-metallic compositions exhibit a metal-core/metal-oxide-shell nanoparticle structure. We furthermore » demonstrate the versatility of this method by incorporating earth-abundant yttrium, resulting in a catalyst with improved precious metal utilization for OER. This method serves as a robust platform for generating ultrasmall (<2 nm) multi-metal particles useful for electrocatalysis research.« less

Water electrolysis is one green approach of storing electrical energy within chemical bonds of the high-energy hydrogen gas (H2). The anodic reaction involved in the oxygen evolution reaction (OER) requires high kinetic overpotential on the overall rate of the process. Recently, plasmonic gold nanoparticles (Au NPs) have been added to enhance the charge transfer at the interface of the OER electrocatalysts and electrolyte under light illumination. However, mechanistic understanding of how Au NPs on the photo-assisted electrochemical process is still lacking. We applied a model system of plasmonic Au electrode and a cobalt (Co)-based OER electrocatalyst in alkaline electrolytes tomore » investigate the plasmon-mediated OER process with (photo)electrochemical and spectroscopic studies. Our results demonstrated that the electrodeposited and surfactant-free plasmonic Au electrode could enhance the electrocatalytic performances of the Co-based electrocatalysts in the OER process with continuous visible and near infrared light illumination. Both the photothermal and energetic charge carriers were found to contribute to the enhanced OER performance based on the transient photocurrent studies, and the interfaces of Au and the Co-based electrocatalysts determined the enhancement mechanisms. The active phase of the cobalt based OER electrocatalyst at operating potentials was identified with electrochemical Raman measurements.« less

Electrocatalytic hydrogen generation requires a multifunctional electrocatalyst with abundant active sites to drive multielectron transfer reactions. High entropy alloys (HEA) are five or more-elements with high configurational entropy are considered unique materials for next-generation electrocatalysts. Here, in this work, based on new screening guidelines for catalyst selections that combine density-functional theory calculated Gibbs formation-enthalpy with bond length and electronegativity variance, a novel HEA electrocatalyst consisting of five elements, namely, Pt, Pd, Ni, Co, and Mn has been designed. By simple room temperature electrodeposition, the designed catalyst is prepared and its hydrogen evolution reaction (HER) is explored and validated through experimentalmore » and theoretical approaches. The HEA demonstrated a superior HER activity with an overpotential of 22.6 mV at -10 mA cm^-2 which outperforms Pt/C commercial catalyst. No evident degradation of the material is detected even after 100 hours of continuous operation under high current density. Moreover, the HEA has shown exceptional performance in harsh electrolyte conditions such as in simulated seawater and actual seawater. Remarkably, the density-functional theory calculated Gibbs formation-enthalpy is small (≈0 eV) compared to Pt/C placing the new HEA near the apex of Trasatti's model of Volcano plot, which is also suggestive of superior HER activity.« less