Concentrating and activating carbon dioxide over AuCu aerogel grain boundaries

Enriched Electrophilic Oxygen Species on Ru Optimize Acidic Water Oxidation

Ruthenium oxide (RuO2) is considered one of the most promising catalysts for replacing iridium oxide (IrO2) in the acidic oxygen evolution reaction (OER). Nevertheless, the performance of RuO2 remains unacceptable due to the dissolution of Ru and the lack of *OH in acidic environments. This paper reports a grain boundary (GB)-rich porous RuO2 electrocatalyst for the efficient and stable acidic OER. The involvement of GB regulates the valence state of Ru and weakens the interaction between Ru and O, effectively facilitating *OH adsorption and *OOH formation. Notably, achieved a record-high catalytic activity (145 mV at 10 mA cm-2) with a low Tafel slope (40.9 mV dec-1) and a remarkable mass activity of 332 mA mg-1 Ru at 1.5 V versus reversible hydrogen electrode is achieved. Additionally, the porous RuO2 exhibits superb stability with an ultra-low degradation rate of 26 µV h-1 over a 50-day durability test. This study opens a viable pathway for the development of efficient and robust Ru-based acidic OER electrocatalysts.

Impact of Surface Composition Changes on the CO2-Reduction Performance of Au-Cu Aerogels

Over the past decades, the electrochemical CO2-reduction reaction (CO2RR) has emerged as a promising option for facilitating intermittent energy storage while generating industrial raw materials of economic relevance such as CO. Recent studies have reported that Au-Cu bimetallic nanocatalysts feature a superior CO2-to-CO conversion as compared with the monometallic components, thus improving the noble metal utilization. Under this premise and with the added advantage of a suppressed H2-evolution reaction due to absence of a carbon support, herein, we employ bimetallic Au3Cu and AuCu aerogels (with a web thickness ≈7 nm) as CO2-reduction electrocatalysts in 0.5 M KHCO3 and compare their performance with that of a monometallic Au aerogel. We supplement this by investigating how the CO2RR-performance of these materials is affected by their surface composition, which we modified by systematically dissolving a part of their Cu-content using cyclic voltammetry (CV). To this end, the effect of this CV-driven composition change on the electrochemical surface area is quantified via Pb underpotential deposition, and the local structural and compositional changes are visually assessed by employing identical-location transmission electron microscopy and energy-dispersive X-ray analyses. When compared to the pristine aerogels, the CV-treated samples displayed superior CO Faradaic efficiencies (≈68 vs ≈92% for Au3Cu and ≈34 vs ≈87% for AuCu) and CO partial currents, with the AuCu aerogel outperforming the Au3Cu and Au counterparts in terms of Au-mass normalized CO currents among the CV-treated samples.

Expanding the Range: AuCu Metal Aerogels from H2O and EtOH

Due to their self-supporting and nanoparticulate structure, metal aerogels have emerged as excellent electrocatalysts, especially in the light of the shift to renewable energy cycles. While a large number of synthesis parameters have already been studied in depth, only superficial attention has been paid to the solvent. In order to investigate the influence of this parameter with respect to the gelation time, crystallinity, morphology, or porosity of metal gels, AuxCuy aerogels were prepared in water and ethanol. It was shown that although gelation in water leads to highly porous gels (60 m2g−1), a CuO phase forms during this process. The undesired oxide could be selectively removed using a post-washing step with formic acid. In contrast, the solvent change to EtOH led to a halving of the gelation time and the suppression of Cu oxidation. Thus, pure Cu aerogels were synthesized in addition to various bimetallic Au3X (X = Ni, Fe, Co) gels. The faster gelation, caused by the lower permittivity of EtOH, led to the formation of thicker gel strands, which resulted in a lower porosity of the AuxCuy aerogels. The advantage given by the solvent choice simplifies the preparation of metal aerogels and provides deeper knowledge about their gelation.

High Performance 3D Self-Supporting Cu-Bi Aerogels for Electrocatalytic Reduction of CO2 to Formate

The electrocatalytic reduction of CO₂ (CO₂ RR) to CO, formate, methane, and other high-value compounds is a promising technique. However, current electrocatalysts suffer from drawbacks such as few active catalytic sites, poor selectivity and low stability, etc, which restrict the practical application. Although monatomic metal catalysts have been widely reported in recent years, high performance non-noble metal aerogels were rarely investigated for electrocatalytic CO₂ RR. Herein, Cu-Bi aerogels with boosted CO₂ RR activity were well constructed by a simple one-step self-assembly method. The resultant Cu₁ Bi₂ exhibits excellent CO₂ RR activity with high faradaic efficiency (FE) of 96.57 % towards HCOOH at a potential of -0.9 V vs. RHE, and the FE_HCOOH remains over 80.18 % in a wide potential window (-0.8 V to -1.2 V vs. RHE). It demonstrated that the enhanced CO₂ RR activity of Cu-Bi aerogels could be attributed to the 3D self-supporting structure of the catalysis, synergistic effect, and low interfacial charge transfer resistance.

Understanding Alkali Contamination in Colloidal Nanomaterials to Unlock Grain Boundary Impurity Engineering

Metal nanogels combine a large surface area, a high structural stability, and a high catalytic activity toward a variety of chemical reactions. Their performance is underpinned by the atomic-level distribution of their constituents, yet analyzing their subnanoscale structure and composition to guide property optimization remains extremely challenging. Here, we synthesized Pd nanogels using a conventional wet chemistry route, and a near-atomic-scale analysis reveals that impurities from the reactants (Na and K) are integrated into the grain boundaries of the poly crystalline gel, typically loci of high catalytic activity. We demonstrate that the level of impurities is controlled by the reaction condition. Based on ab initio calculations, we provide a detailed mechanism to explain how surface-bound impurities become trapped at grain boundaries that form as the particles coalesce during synthesis, possibly facilitating their decohesion. If controlled, impurity integration into grain boundaries may offer opportunities for designing new nanogels.

Au aerogel for selective CO2electroreduction to CO: ultrafast preparation with high performance

Noble metal aerogels (NMAs) have been used in a variety of (photo-)electrocatalytic reactions, but pure Au aerogel (AG) has not been used in CO₂electroreduction to date. To explore the potential application in this direction, AG was prepared to be used as the cathode in CO₂electroreduction to CO. However, the gelation time of NMAs is usually very long, up to several weeks. Here, an excess NaBH₄and turbulence mixing-promoted gelation approach was developed by introducing magnetic stirring as an external force field, which therefore greatly shortened the formation time of Au gels to several seconds. The AG-3 (AG with Au loading of 0.003 g) exhibited a high CO Faradaic efficiency (FE) of 95.6% at an extremely low overpotential of 0.39 V, and over 91% of CO FE was reached in a wide window of -0.4 to -0.7 V versus the reversible hydrogen electrode (RHE). Partial current density in CO was measured to be -19.35 mA cm^-2at -0.8 V versus RHE under 1 atm of CO₂. The excellent performance should be ascribed to its porous structure, abundant active sites, and large electrochemical active surface area. It provides a new method for preparation of AG with ultrafast gelation time and large production at room temperature, and the resulting pure AG was for the first time used in the field of CO₂electroreduction.

Ag-Cu aerogel for electrochemical CO2 conversion to CO

The current strategy of electrocatalytic CO₂ reduction reaction (eCO₂RR) to generate useful chemicals and hydrocarbons is supposed to effectively mitigate the greenhouse effect. The practical application for eCO₂RR in aqueous solutions, however, still was encumbered by its high overpotential, low activity and poor selectivity due to CO₂ mass transfer and intermediate stability. Electrocatalytic materials with reduced overpotential and high efficiency and selectivity are exploited for further development. Herein, Ag⁺ and Cu²⁺ precursors were co-reduced to generate Ag-Cu bimetallic aerogel after further freeze drying. Compared with Ag₁₀₀ aerogel, the optimal Ag₈₈Cu₁₂ can effectively decrease overpotential, improve selectivity and current density, and keep electrochemical stability. At -0.89 V vs. RHE, the Faraday efficiency reached 89.40% and the CO partial current density of -5.86 mA cm^-2 was obtained. The intrinsic property of metal aerogel (hydrophobic, hierarchical porous structure, conductivity), presence of rich grain boundaries and geometric effect and the introduction of Cu leading to improvement of adsorption between the catalyst and the *COOH intermediate in Ag₈₈Cu₁₂, contribute to the enhanced performance. Furthermore, the strategy of constructing metal aerogel will improve metal catalyst performance towards eCO₂RR and pave way for further industrial applications.

Preparation and Electrocatalysis Application of Pure Metallic Aerogel: A Review

Nanomaterials are widely used in electrocatalysts due to their quantum size effect and high utilization efficiency. There are two ways to improve the activity of nanoelectrocatalysts: increasing the number of active sites and improving the inherent activity of each catalytic site. The structure of the catalyst itself can be improved by increasing the number of exposed active sites per unit mass. The high porosity and three-dimensional network structure enable aerogels to have the characteristics of a large specific surface area, exposing many active sites and bringing structural stability through the self-supporting nature of aerogels. Thus, by adjusting the compositions of aerogels, the synergetic effect introduced by alloy elements can be utilized to further improve the single-site activity. In this review, we summarized the basic preparation strategy of aerogels and extended it to the preparation of alloys and special structure aerogels. Moreover, through the eight electrocatalysis cases, the outstanding catalytic performances and broad applicability of aerogel electrocatalysts are emphasized. Finally, we predict the future development of pure metallic aerogel electrocatalysts from the perspective of preparation to application.