Crystal and Electronic Structure Modification of Synthetic Perryite Minerals: A Facile Phase Transformation Strategy to Boost the Oxygen Evolution Reaction

Geometry effect and electronic effect are both essential for the rational design of a highly efficient electrocatalyst. In order to untangle the relationship between these effects and electrocatalytic activity, the perryite phase with a versatile chemical composition, (NixFe1–x)8(TyP1–y)3 (T = Si and Ge; 1 ≥ x, y ≥ 0), was selected as a platform to demonstrate the influence of geometry (e.g., atomic size and bond length) and electronic (e.g., bond strength and bonding scheme) factors toward the oxygen evolution reaction (OER). It was realized that the large Ge atom in the perryite phase can expand the unit cell parameters and interatomic distances (i.e., weaken bond strengths), which facilitates the phase transformation into active metal oxyhydroxide during OER. The quaternary perryite phase, Ni7FeGeP2, displays excellent OER activity and achieves current densities of 20 and 100 mA/cm2 at overpotentials of 239 and 273 mV, respectively. The oxidation state of Ni and Fe in the perryite phase before/after OER was analyzed and discussed. The result suggests that incorporating the Fe element in the system may increase the rate constant of OER (KOER) and therefore keeps the Ni element in a low valance state (i.e., Ni2+). This work indicates that the manipulation of geometry and electronic factors can promote phase transformation as well as OER activity, which exemplifies a strategy to design a promising “precatalyst” for OER

Synergistic-Effect-Controlled CoTe₂/Carbon Nanotube Hybrid Material for Efficient Water Oxidation

In anode, electrocatalytic water splitting involves oxygen evolution reaction (OER), which is a complex and sluggish reaction, and thus the efficiency to produce hydrogen is seriously limited by OER. We report that CoTe₂ exhibits optimized OER activity for the first time. Multiwalled carbon nanotube (MWCNT) is utilized to support CoTe₂ in generating a synergistic effect to enhance OER activity and improve stability by tuning different loading amounts of CoTe₂ on CNT. In 1.0 M KOH, bare CoTe₂ needed overpotential of 323 mV to produce 10 mA/cm² with Tafel slope of 85.1 mV/dec, but CoTe₂/carbon nanotube (CNT) with optimized loading amount of CoTe₂ required only 291 mV to produce10 mA/cm² with Tafel slope of 44.2 mV/dec. X-ray absorption near edge structure (XANES) was applied to prove that an electron transfer from e_g band of CoTe₂ to CNT caused a synergistic effect. This electron transfer modulated the bond strength of oxygen-related intermediate species on the surface of catalyst and optimized OER performance. In situ XANES was used to compare CoTe₂/CNT and pristine CoTe₂ during OER. It proved the transition state of CoOOH more easily existed by adding CNT in hybrid material during OER to enhance the efficiency of OER. Moreover, bare CoTe₂ is unstable under OER, but the CoTe₂/CNT hybrid materials exhibited improved and exceptional durability by time-dependent potentiostatic electrochemical measurement for 24 h and continuous cyclic voltammetry for 1000 times. Our result suggests that this new OER electrocatalyst for OER can be applied in various water-splitting devices and can promote hydrogen economy

Sulfur-Stabilizing Ultrafine High-Entropy Alloy Nanoparticles on MXene for Highly Efficient Ethanol Electrooxidation

High-entropy alloys (HEAs) are significantly promising candidates for heterogeneous catalysis, yet the controllable synthesis of ultrafine HEA nanoparticles (NPs) remains a formidable challenge due to severe thermal sintering during the high-temperature fabrication process. Herein, we report a sulfur-stabilizing strategy to construct ultrafine HEA NPs with an average diameter of 4.02 nm supported on sulfur-modified Ti3C2Tx (S–Ti3C2Tx) MXene, on which the strong interfacial metal–sulfur interactions between HEA NPs and the S–Ti3C2Tx supports significantly increase the interfacial adhesion strength, thus greatly suppressing nanoparticle sintering by retarding both particle migration and metal atom diffusion. The representative quinary PtPdCuNiCo HEA–S–Ti3C2Tx exhibits excellent catalytic performance toward alkaline ethanol oxidation reaction (EOR) with an ultrahigh mass activity of 7.03 A mgPt+Pd–1, which is 4.34 and 5.17 times higher than those of the commercial Pt/C and Pd/C catalysts, respectively. In situ attenuated total reflection–infrared spectroscopy studies reveal that the high intrinsic catalytic activity for the EOR can be ascribed to the synergy of different catalytically active sites of HEA NPs and the well-designed interfacial metal–sulfur interactions

Turn the Trash into Treasure: Egg-White-Derived Single-Atom Electrocatalysts Boost Oxygen Reduction Reaction

Egg provides human beings the nutrition and economical products, such as antimicrobial and cosmetics. However, we mainly employ egg yolk, causing tons of egg white as the industrial waste to be further reprocessed. On account of the sustainable issue, we adopt the egg white to prepare single-atom electrocatalysts, achieving a half-wave potential (E1/2) of 0.927 V vs reversible hydrogen electrode (RHE) for oxygen reduction reaction, overperforming the commercial Pt/C (0.857 V) and the conventional iron single-atom electrocatalyst (0.835 V). Using in situ X-ray absorption spectroscopy (XAS) studies and density functional theory (DFT) calculations, we decrypt that electrons transfer through the dyz­(dxz) orbitals in egg-white-derived single-atom electrocatalysts, facilitating their hybridization with the p orbital in oxygen, reducing the energy barrier in the rate-determining step, and boosting the overall catalytic activity. Our discovery provides an alternative perception to turn trash into treasure and promote sustainability

A General Strategy for Engineering Single-Metal Sites on 3D Porous N, P Co-Doped Ti₃C₂T_X MXene

Two-dimensional (2D) MXenes have been developed to stabilize single atoms via various methods, such as vacancy reduction and heteroatom-mediated interactions. However, anchoring single atoms on 3D porous MXenes to further increase catalytic active sites and thus construct electrocatalysts with high activity and stability remains unexplored. Here, we reported a general synthetic strategy for engineering single-metal sites on 3D porous N, P codoped Ti3C2TX nanosheets. Through a “gelation-and-pyrolysis” process, a series of atomically dispersed metal catalysts (Pt, Ir, Ru, Pd, and Au) supported by N, P codoped Ti3C2TX nanosheets with 3D porous structure can be obtained and serve as efficient catalysts for the electrochemical hydrogen evolution reaction (HER). As a result of the favorable electronic and geometric structure of N­(O), P-coordinated metal atoms optimizing catalytic intermediates adsorption and 3D porous structure exposing the active surface sites and facilitating charge/mass transfer, the as-synthesized Pt SA-PNPM catalyst shows ∼20-fold higher activity than the commercial Pt/C catalyst for electrochemical HER over a wide pH range

Wide Range pH-Tolerable Silicon@Pyrite Cobalt Dichalcogenide Microwire Array Photoelectrodes for Solar Hydrogen Evolution

This study employed silicon@cobalt dichalcogenide microwires (MWs) as wide range pH-tolerable photocathode material for solar water splitting. Silicon microwire arrays were fabricated through lithography and dry etching technologies. Si@Co­(OH)₂ MWs were utilized as precursors to synthesize Si@CoX₂ (X = S or Se) photocathodes. Si@CoS₂ and Si@CoSe₂ MWs were subsequently prepared by thermal sulfidation and hydrothermal selenization reaction of Si@Co­(OH)₂, respectively. The CoX₂ outer shell served as cocatalyst to accelerate the kinetics of photogenerated electrons from the underlying Si MWs and reduce the recombination. Moreover, the CoX₂ layer completely deposited on the Si surface functioned as a passivation layer by decreasing the oxide formation on Si MWs during solar hydrogen evolution. Si@CoS₂ photocathode showed a photocurrent density of −3.22 mA cm^–2 at 0 V (vs RHE) in 0.5 M sulfuric acid electrolyte, and Si@CoSe₂ MWs revealed moderate photocurrent density of −2.55 mA cm^–2. However, Si@CoSe₂ presented high charge transfer efficiency in neutral and alkaline electrolytes. Continuous chronoamperometry in acid, neutral, and alkaline solutions was conducted at 0 V (vs RHE) to evaluate the photoelectrochemical durability of Si@CoX₂ MWs. Si@CoS₂ electrode showed no photoresponse after the chronoamperometry test because it was etched through the electrolyte. By contrast, the photocurrent density of Si@CoSe₂ MWs gradually increased to −5 mA cm^–2 after chronoamperometry characterization owing to the amorphous structure generation

Spontaneously Sn-Doped Bi/BiO_<i>x</i> Core–Shell Nanowires Toward High-Performance CO₂ Electroreduction to Liquid Fuel

Electrochemical CO2 reduction provides a promising strategy to product value-added fuels and chemical feedstocks. However, it remains a grand challenge to further reduce the overpotentials and increase current density for large-scale applications. Here, spontaneously Sn doped Bi/BiOx nanowires (denoted as Bi/Bi­(Sn)­Ox NWs) with a core–shell structure were synthesized by an electrochemical dealloying strategy. The Bi/Bi­(Sn)­Ox NWs exhibit impressive formate selectivity over 92% from −0.5 to −0.9 V versus reversible hydrogen electrode (RHE) and achieve a current density of 301.4 mA cm–2 at −1.0 V vs RHE. In-situ Raman spectroscopy and theoretical calculations reveal that the introduction of Sn atoms into BiOx species can promote the stabilization of the *OCHO intermediate on the Bi­(Sn)­Ox surface and suppress the competitive H2/CO production. This work provides effective in situ construction of the metal/metal oxide hybrid composites with heteroatom doping and new insights in promoting electrochemical CO2 conversion into formate for practical applications

Combining Electrospinning and Hydrothermal Methods to Prepare Bi₂S₃@SiO₂ Nanostructure-Based Membranes for Enhanced Capture Capacity of Off-Gas Iodine from a Nuclear Plant

As the main fission products of nuclear power plants, radioactive iodine isotopes are of great concern because of their great harm to public safety. In this work, a nanocomposite of bismuth sulfide coated with the electrospinning SiO2 nanofibers with a diameter of about 280 nm nanostructure-based membranes (Bi2S3@SiO2) was successfully prepared to dispose of gaseous iodine. Results showed that the adsorption capacity of Bi2S3@SiO2 for iodine can be up to 1180 mg g–1, which is higher than the commercial silver-exchanged zeolite (AgZ) and other bismuth-based adsorbents. Chemisorption is the major adsorption behavior of iodine capture. Thermogravimetric analysis results demonstrated that the Bi2S3@SiO2 nanocomposites were stable up to 300 °C before and after capturing iodine. X-ray diffraction results revealed that BiSI was initially formed and then transformed to BiI3. Scanning electron microscopy revealed that the sulfur element remains in the samples after interacting with iodine, and X-ray absorption near-edge spectra further confirmed that its oxidation states are a mixture of S0, S3+, and S6+. The oxidation states of bismuth and iodine are Bi3+ and I–, respectively, revealed by X-ray photoelectron spectroscopy. The reactions between Bi2S3@SiO2 nanocomposites and I2 vapor are as follows: I2 was reduced to be I– and the BiI3 crystalline phase is the final form; S2– in Bi2S3 was oxidized to higher valences (S0, S3+, and S6+), and amorphous phases are their final forms. The research results demonstrated that the nanostructure-based membranes prepared by this work would be a promising candidate nanomaterial for capturing iodine in the plant off-gas streams

Dealloying-Induced Zeolite-like Metal Framework of AB₂ Laves Phase Intermetallic Electrocatalysts

Exploring an efficient and robust electrocatalyst for hydrogen evolution reaction (HER) at high pH and temperature holds the key to the industrial application of alkaline water electrolysis (AWE). Herein, we design an open tunnel structure by dealloying a series of Laves phase intermetallics, i.e., MCo2 and MRu0.25Co1.75 (M = Sc and Zr). The dealloying process can induce a zeolite-like metal framework for ScCo2 and ScRu0.25Co1.75 by stripping Sc metal from the center of a tunnel structure. This structural engineering significantly lowers their overpotentials at a current density of 500 mA/cm2 (η500) ca. 80 mV in 1.0 M KOH. Through a simple process, ScRu0.25Co1.75 can be easily decorated on a carbon cloth substrate and only requires 132 mV to reach 500 mA/cm2. More importantly it can maintain activity over 1000 h in industrial conditions (6.0 M KOH at 333 K), showing its potential for practical industrial applications