A universal and scalable transformation of bulk metals into single-atom catalysts in ionic liquids.

Single-atom catalysts (SACs) with maximized metal atom utilization and intriguing properties are of utmost importance for energy conversion and catalysis science. However, the lack of a straightforward and scalable synthesis strategy of SACs on diverse support materials remains the bottleneck for their large-scale industrial applications. Herein, we report a general approach to directly transform bulk metals into single atoms through the precise control of the electrodissolution-electrodeposition kinetics in ionic liquids and demonstrate the successful applicability of up to twenty different monometallic SACs and one multimetallic SAC with five distinct elements. As a case study, the atomically dispersed Pt was electrodeposited onto Ni3N/Ni-Co-graphene oxide heterostructures in varied scales (up to 5 cm × 5 cm) as bifunctional catalysts with the electronic metal-support interaction, which exhibits low overpotentials at 10 mA cm-2 for hydrogen evolution reaction (HER, 30 mV) and oxygen evolution reaction (OER, 263 mV) with a relatively low Pt loading (0.98 wt%). This work provides a simple and practical route for large-scale synthesis of various SACs with favorable catalytic properties on diversified supports using alternative ionic liquids and inspires the methodology on precise synthesis of multimetallic single-atom materials with tunable compositions.

Temperature and Pressure Effects on Unrecoverable Voids in Li Metal Solid-State Batteries.

All-solid-state batteries (ASSB) can potentially achieve high gravimetric and volumetric energy densities (900 Wh/L) if paired with a lithium metal anode and solid electrolyte. However, there is a lack in critical understanding about how to operate lithium metal cells at high capacities and minimize unwanted degradation mechanisms such as dendrites and voids. Herein, we investigate how pressure and temperature influence the formation and annihilation of unrecoverable voids in lithium metal upon stripping. Stack pressure and temperature are effective means to initiate creep-induced void filling and decrease charge transfer resistances. Applying stack pressure enables lithium to deform and creep below the yield stress during stripping at high current densities. Lithium creep is not sufficient to prevent cell shorting during plating. Three-electrode experiments were employed to probe the kinetic and morphological limitations that occur at the anode-solid electrolyte during high-capacity stripping (5 mAh/cm2). The role of cathode-LLZO interface, which dictates cyclability and capacity retention in full cells, was also studied. This work elucidates the important role that temperature (external or in situ generated) has on reversible operation of solid-state batteries.

Dynamic Electrolyte Spreading during Meniscus-Confined Electrodeposition and Electrodissolution of Copper for Surface Patterning.

Meniscus-confined electrodeposition and electrodissolution are a facile maskless approach to generate controlled surface patterns and 3D microstructures. In these processes, the solid-liquid interfacial area confined by the meniscus dictates the zone on which the electrodeposition or the electrodissolution occurs. In this work, we show that the process of electrodeposition or electrodissolution in a meniscus-confined droplet system can lead to dynamic spreading of the meniscus, thereby changing the solid-liquid interfacial area confined by the meniscus. Our results show that the wetting dynamics depends on the applied voltage and the type of interface underneath the droplet, specifically a smooth surface with a homogeneous solid-liquid interface or a superhydrophobic surface with a heterogeneous solid-liquid and liquid-vapor interface. It is found that both electrodissolution and electrodeposition processes induced droplet spreading in the case of a smooth surface with a homogeneous interface. However, a superhydrophobic surface with a heterogeneous interface under the droplet produced nonlinear spreading during electrodissolution and spreading inhibition during electrodeposition. The underlying mechanisms resulting in the observed behavior have been explicated. The dynamic droplet spreading could modify the dimensions of the patterns formed and hence is of immense importance to the meniscus-confined electrochemical micromachining. The findings also provide fundamental insights into the spreading behavior and wetting transitions induced by electrochemical reactions.

Anodic electrodissolution: a low-cost alternative for carbon steel sample preparation for quantification of metals by ICP-MS.

A fast and low-cost method using electrolysis for sample preparation of carbon steel present in weld electrodes aiming to achieve quantification of heavy metals by inductively coupled plasma mass spectrometry (ICP-MS) was developed. Conditions of the electrolysis, such as pH and electrical charge were investigated to improve the solubility and concentration of the analytes in the electrolyte. The method showed high reproducibility, with a relative standard deviation (RSD) of less than 3.05%, and the recovery from 88.6 to 108.9% for the analytes demonstrates the accuracy of the developed method.

Hot Holes Assist Plasmonic Nanoelectrode Dissolution.

Strong light-absorbing properties allow plasmonic metal nanoparticles to serve as antennas for other catalysts to function as photocatalysts. To achieve plasmonic photocatalysis, the hot charge carriers created when light is absorbed must be harnessed before they decay through internal relaxation pathways. We demonstrate the role of photogenerated hot holes in the oxidative dissolution of individual gold nanorods with millisecond time resolution while tuning charge-carrier density and photon energy using snapshot hyperspectral imaging. We show that light-induced hot charge carriers enhance the rate of gold oxidation and subsequent electrodissolution. Importantly, we distinguish how hot holes generated from interband transitions versus hot holes around the Fermi level contribute to photooxidative dissolution. The results provide new insights into hot-hole-driven processes with relevance to photocatalysis while emphasizing the need for statistical descriptions of nonequilibrium processes on innately heterogeneous nanoparticle supports.

Pt-C Interfaces Based on Electronegativity-Functionalized Hollow Carbon Spheres for Highly Efficient Hydrogen Evolution.

The hydrogen evolution reaction activity of carbon-supported Pt catalyst is highly dependent on Pt-C interfaces. Herein, we focus on the relationships between Pt activity and N/O-functionalized hollow carbon sphere (HCS) substrate in acidic media. The electrochemical dissolution of Pt counter electrode is performed to prepare Pt nanoparticles in low loading. The N groups are beneficial for homogeneously sized Pt nanoparticles, whereas the O groups lead to aggregated nanoparticles. Moreover, the proper electronegativity of the N groups may enable capturing of protons to create proton-rich Pt-C interfaces and transfer them onto the Pt sites. The O groups may also capture protons by hydrogen bonding, but the subsequent release of protons is more difficult due to a stronger electronegativity and result in an inferior Pt activity. Consequently, the N-doped HCS with a low Pt loading (1.7 µg cm-2 and 0.05 wt %) possesses a higher intrinsic activity compared with Pt on O-doped HCS. Moreover, it outperforms the commercial 20% Pt/C with a stable operation for 12 h. This work may provide suggestions for constructing the advantageous Pt-C interfaces by proper functional groups for high catalytic efficiencies.

Anodic passivation on the recycling of cemented carbide scrap by selective electro-dissolution.

Selective dissolution is an effective method to recycle WC and Co from cemented carbide scrap, and the electro-dissolution process is considered competitive. However, the anodic passivation slows down oxidation and leads to inefficiency during electrolysis. The porosity of the WC coat is the main impact factor for passivation. Thus, in this study, types of WC-Co cemented carbide (YG8/YG15/YG20) with different bonding phase content were studied in the acid electrolyte through electrochemistry tests. The thickness of the coat was measured, and the diffusion coefficients (Di) were calculated by Fick's first law of diffusion. The Di of cation was 0.088 × 10-10, 0.61 × 10-10, 0.70 × 10-10 m2 s-1 for YG8, YG15, YG20, respectively. The inferior diffusion coefficient resulting from the dense coat was believed to be the main reason for the low dissolving rate.

Deciphering the Elementary Steps of Transport-Reaction Processes at Individual Ag Nanoparticles by 3D Superlocalization Microscopy.

Transport-reaction processes at individual Ag nanoparticles (NPs) are studied using electrochemistry coupled with in situ 3D light scattering microscopy. Electrochemistry is used to trigger a (i) diffusiophoretic transport mode capable of accelerating and preconcentrating NPs toward an electrode and (ii) subsequent diffusion-controlled oxidation of NPs. Individual NP dissolution rate, analyzed using optical modeling, suggests the intervention of insoluble products. New insights into diverse NPs behaviors highlight the strength of coupled optical-electrochemical 3D microscopies for single-NP studies.

Struvite precipitation and phosphorus removal using magnesium sacrificial anode.

Struvite precipitation using magnesium sacrificial anode as the only source of magnesium is presented. High-purity magnesium alloy cast anode was found to be very effective in recovery of high-quality struvite from water solutions and from supernatant of fermented waste activated sludge from a wastewater treatment plant that does not practice enhanced biological phosphorus removal. Struvite purity was strongly dependent on the pH and the electric current density. Optimum pH of the 24 mM phosphorus and 46 mM ammonia solution (1:1.9 P:N ratio) was in the broad range between 7.5 and 9.3, with struvite purity exceeding 90%. Increasing the current density resulted in elevated struvite purity. No upper limits were observed in the studied current range of 0.05-0.2 A. Phosphorus removal rate was proportional to the current density and comparable for tests with water solutions and with the supernatant from fermented sludge. The highest P-removal rate achieved was 4.0 mg PO4-P cm(-2) h(-1) at electric current density of 45 A m(-2). Initial substrate concentrations affected the rate of phosphorus removal. The precipitated struvite accumulated in bulk liquid with significant portions attached to the anode surface from which regular detachment occurred.