Synthesis of popcorn-shaped gallium-platinum (GaPt3) nanoparticles as highly efficient and stable electrocatalysts for hydrogen evolution reaction

Metalloid tellurium-induced electron-deficient NiFe alloys awakening efficient oxygen electroreduction

Transition metal alloys catalysts have been extensively studied in oxygen reduction reactions (ORR); however, their suboptimal catalytic activity presents a significant challenge. Modifying the local electronic configuration of the catalytic active site by heteroatom doping is an effective strategy to enhance the electrocatalytic performance. Herein, an ORR Te/NiFe@NCNFs electrocatalyst, featuring with Te modified NiFe alloys nanoparticles and anchored on N-doped carbon nanofibers (NCNFs), was constructed via a surface-modified synthesis strategy. The introduction of Te leads to electron transfer on the surface of Te/NiFe@NCNFs, forming an electron-deficient NiFe site with high catalytic activity. Theoretical calculations confirm that Te regulates an electron redistribution and reduces the d-band centers of Fe and Ni, which help to facilitate the desorption of ORR intermediate oxides. As a result, Te/NiFe@NCNFs exhibit a half-wave potential of 0.86 V, superior to that of Pt/C (0.84 V) and most reported modified-NiFe-based catalysts. When assembled into a zinc-air battery, Te/NiFe@NCNFs deliver remarkable power density of 158.8 mW cm-2-2 and specific capacity of 778.1 mA h gZn-1. The present study presents new insights into the modulation of electronic structure in transition metal alloys, providing a feasible and innovative approach for the design of unrivaled ORR electrocatalysts.

Aluminum-incorporation activates vanadium carbide with electron-rich carbon sites for efficient pH-universal hydrogen evolution reaction

Vanadium carbide (VC) is the greatest potential hydrogen evolution reaction (HER) catalyst because of its platinum-like property and abundant earth reserves. However, it exhibits insufficient catalytic performance due to the unfavorable interaction of reaction intermediates with catalysts. In this work, using NH4VO3 as the main raw material, the flow ratio of CH4 to Ar was accurately controlled, and a non-transition metal Al-doped into VC (100) nano-flowers with carbon hybrids on nickel foams (Al-VC@C/NF) was prepared for the first time as a high-efficiency HER catalyst by chemical vapor carbonization. The overpotential of Al-VC@C/NF catalysts in 0.5 M H2SO4 and 1 M KOH at a current density of 10 mA cm-2 are only 58 mV and 97 mV, respectively, which are the best HER performance among non-noble metal vanadium carbide based catalysts. Simultaneously, Al-VC@C/NF exhibits small Tafel slope (45 mV dec-1 and 73 mV dec-1) and excellent stability in acidic and alkaline media. Theoretical calculations demonstrate that doped Al atoms can induce electron redistribution on the vanadium carbide surface to form electron-rich carbon sites, which significantly reduces the energy barrier during the HER process. This work provides a new tactic to modulate vanadium-based carbons as efficient HER catalysts through non-transition metal doping.

Activated platinum in gallium-based room-temperature liquid metals for enhanced reduction reactions

Room-temperature gallium-based liquid metals (LMs) have recently attracted significant attention worldwide for application in catalysis because of their unique combination of fluidic and catalytic properties. Platinum loading in LMs is expected to enhance the catalytic performance of various reaction systems. However, Pt-loaded methods for Ga-based LMs have not yet been sufficiently developed to improve the catalytic performance and Pt utilization efficiency. In this study, a novel method for the fabrication of Pt-incorporated LMs using Pt sputter deposition (Pt(dep)-LMs) was developed. The Pt(dep)-LMs contained well-dispersed Pt flakes with diameters of 0.89 ± 0.6 μm. The catalytic activity of the Pt(dep)-LM with a Pt loading of ∼0.7 wt% was investigated using model reactions such as methylene blue (MB) reduction and hydrogen production in an acidic aqueous solution. The Pt(dep)-LMs showed a higher MB reduction rate (three times) and hydrogen production (three times) than the LM loaded with conventional Pt black (∼0.7 wt%). In contrast to the Pt(dep)-LMs, solid-based Ga with a Pt loading of ∼0.7 wt% did not catalyze the reactions. These results demonstrate that Pt activation occurred in the Pt(dep)-LMs fabricated by Pt sputtering, and that the fluidic properties of the LMs enhanced the catalytic reduction reactions. Thus, these findings highlight the superior performance of the Pt deposition method and the advantages of using Pt-LM-based catalysts.

Ga-Modification Near-Surface Composition of Pt-Ga/C Catalyst Facilitates High-Efficiency Electrochemical Ethanol Oxidation through a C2 Intermediate

In electrochemical ethanol oxidation reactions (EOR) catalyzed by Pt metal nanoparticles through a C2 route, the dissociation of the C-C bond in the ethanol molecule can be a limiting factor. Complete EOR processes producing CO2 were always exemplified by the oxidative dehydrogenation of C1 intermediates, a reaction route with less energy utilization efficiency. Here, we report a Pt3Ga/C electrocatalyst with a uniform distribution of Ga over the nanoparticle surface for EOR that produces CO2 at medium potentials (>0.3 V vs SCE) efficiently through direct and sustainable oxidation of C2 intermediate species, i.e., acetaldehyde. We demonstrate the excellent performance of the Pt3Ga-200/C catalyst by using electrochemical in situ Fourier transform infrared reflection spectroscopy (FTIR) and an isotopic labeling method. The atomic interval structure between Pt and Ga makes the surface of nanoparticles nonensembled, avoiding the formation of poisonous *CHx and *CO species via bridge-type adsorption of ethanol molecules. Meanwhile, the electron redistribution from Ga to Pt diminishes the *O/*OH adsorption and CO poisoning on Pt atoms, exposing more available sites for interaction with the C2 intermediates. Furthermore, the dissociation of H2O into *OH is facilitated by the high hydrophilicity of Ga, which is supported by DFT calculations, promoting the deep oxidation of C2 intermediates. Our work represents an extremely rare EOR process that produces CO2 without observing kinetic limitations under medium potential conditions.

A comprehensive review on the electrochemical parameters and recent material development of electrochemical water splitting electrocatalysts

Electrochemical splitting of water is an appealing solution for energy storage and conversion to overcome the reliance on depleting fossil fuel reserves and prevent severe deterioration of the global climate. Though there are several fuel cells, hydrogen (H2) and oxygen (O2) fuel cells have zero carbon emissions, and water is the only by-product. Countless researchers worldwide are working on the fundamentals, i.e. the parameters affecting the electrocatalysis of water splitting and electrocatalysts that could improve the performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and overall simplify the water electrolysis process. Noble metals like platinum for HER and ruthenium and iridium for OER were used earlier; however, being expensive, there are more feasible options than employing these metals for all commercialization. The review discusses the recent developments in metal and metalloid HER and OER electrocatalysts from the s, p and d block elements. The evaluation perspectives for electrocatalysts of electrochemical water splitting are also highlighted.

Low-temperature liquid platinum catalyst

Insights into metal-matrix interactions in atomically dispersed catalytic systems are necessary to exploit the true catalytic activity of isolated metal atoms. Distinct from catalytic atoms spatially separated but immobile in a solid matrix, here we demonstrate that a trace amount of platinum naturally dissolved in liquid gallium can drive a range of catalytic reactions with enhanced kinetics at low temperature (318 to 343 K). Molecular simulations provide evidence that the platinum atoms remain in a liquid state in the gallium matrix without atomic segregation and activate the surrounding gallium atoms for catalysis. When used for electrochemical methanol oxidation, the surface platinum atoms in the gallium-platinum system exhibit an activity of [Formula: see text] three orders of magnitude higher than existing solid platinum catalysts. Such a liquid catalyst system, with a dynamic interface, sets a foundation for future exploration of high-throughput catalysis.

Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells

[Figure: see text].

Perspective on intermetallics towards efficient electrocatalytic water-splitting

Intermetallic compounds exhibit attractive electronic, physical, and chemical properties, especially in terms of a high density of active sites and enhanced conductivity, making them an ideal class of materials for electrocatalytic applications. Nevertheless, widespread use of intermetallics for such applications is often limited by the complex energy-intensive processes yielding larger particles with decreased surface areas. In this regard, alternative synthetic strategies are now being explored to realize intermetallics with distinct crystal structures, morphology, and chemical composition to achieve high performance and as robust electrode materials. In this perspective, we focus on the recent advances and progress of intermetallics for the reaction of electrochemical water-splitting. We first introduce fundamental principles and the evaluation parameters of water-splitting. Then, we emphasize the various synthetic methodologies adapted for intermetallics and subsequently, discuss their catalytic activities for water-splitting. In particular, importance has been paid to the chemical stability and the structural transformation of the intermetallics as well as their active structure determination under operating water-splitting conditions. Finally, we describe the challenges and future opportunities to develop novel high-performance and stable intermetallic compounds that can hold the key to more green and sustainable economy and rise beyond the horizon of water-splitting application.

Atomically dispersed Ru in Pt3Sn intermetallic alloy as an efficient methanol oxidation electrocatalyst

We successfully fabricate a novel concave nanostructure that is composed of atomically dispersed Ru atoms in Pt₃Sn nanoconcaves (Ru-Pt₃Sn NCs), which shows enhanced performance in methanol electroxidation compared to commercial Pt/C. This could be ascribed to the stable intermetallic structure and active surface structure, as well as the synergy among Pt, Sn and Ru.

Synthesis of raspberry-like antimony-platinum (SbPt) nanoparticles as highly active electrocatalysts for hydrogen evolution reaction

Binary transition metals can facilitate the hydrogen evolution reaction (HER) through the synergistic integration of different electrochemical properties. To determine binary transition metals that are highly active, Greely et al. conducted a simulation of 256 different binary transition metals. They demonstrated that BiPt, PtRu, AsPt, SbPt, BiRh, RhRe, PtRe, AsRu, IrRu, RhRu, IrRe, and PtRh could be used as efficient electrocatalysts for HER. However, only few of them are synthesized and used as electrocatalysts. In this work, we report the synthesis of the raspberry-like antimony-platinum (SbPt) nanoparticles (NPs) via a colloidal nanocrystal synthesis. These NPs exhibited efficient activity with a low overpotential of 27 mV to reach 10 mA cm^-2 in acidic media. We conducted long-term durability test for 90,000 s under an applied voltage of 0.5 V (vs. RHE) and cycling tests of over 10,000 cycles under an applied voltage of 0.1 to -0.5 V (vs. RHE). The high activity exhibited by the raspberry-like SbPt NPs may be due to the following reasons: (1) the raspberry-like SbPt NPs exhibited versatile active exposed (110), (100), (101), and (012) facets as efficient HER catalysts, and (2) as confirmed by both the density functional theory (DFT) simulation and experimental results, the presence of Sb 3d subsurface broadened the Pt surface d-band, which caused synergistic effects on water splitting. In summary, synthesis of the new colloidal raspberry-like SbPt NPs is essential to elucidate the fundamental properties of the nanomaterial and nanostructure design. This study could facilitate the development of Pt-group materials that can be used as HER catalysts.

Amide-Assisted Synthesis of Iron Germanium Sulfide (Fe2GeS4) Nanostars: The Effect of LiN(SiMe3)2 on Precursor Reactivity for Favoring Nanoparticle Nucleation or Growth

Olivine Fe₂GeS₄ has been identified as a promising photovoltaic absorber material introduced as an alternate candidate to iron pyrite, FeS₂. The compounds share similar benefits in terms of elemental abundance and relative nontoxicity, but Fe₂GeS₄ was predicted to have higher stability with respect to decomposition to alternate phases and, therefore, more optimal device performance. Our initial report of the nanoparticle (NP) synthesis for Fe₂GeS₄ was not well understood and required an inefficient 24 h growth to dissolve an iron sulfide impurity. Here, we report an amide-assisted Fe₂GeS₄ NP synthesis that directly forms the phase-pure product in minutes. This significant advance was achieved by the replacement of the poorly understood hexamethyldisilazane (HMDS) additive and TMS₂S by the conjugate base, lithium bis(trimethylsilyl)amide (LiN(SiMe₃)₂), and elemental S, respectively. We hypothesized that fragments of both TMS₂S and HMDS had carried out the roles that Brønsted bases play in amide-assisted NP syntheses and were necessary for Ge incorporation. Convolution of this role with the supply of S in TMS₂S caused the iron sulfide impurities. Separating these effects in the use of LiN(SiMe₃)₂ and elemental S resulted in synthetic control over the ternary phase. Herein we explore the Fe-Ge-S reaction landscape and the role of the base. Its concentration was found to increase the reactivities of the Fe, Ge, and S precursors, and we discuss possible metal-amide intermediates. This affords tunability in two areas: favorability of NP nucleation versus growth and phase formation. The phase-purity of Fe₂GeS₄ depends on the molar ratios of the cations, base, and amine as well as the Fe:Ge:S molar ratios. The resultant Fe₂GeS₄ NPs exhibit an interesting star anise-like morphology with stacks of nanoplates that intersect along a 6-fold rotation axis. The optical properties of the Fe₂GeS₄ NPs are consistent with previously published measurements showing a measured band gap of 1.48 eV.

Platinum Atoms and Nanoparticles Embedded Porous Carbons for Hydrogen Evolution Reaction

Due to the growing demand for energy and imminent environmental issues, hydrogen energy has attracted widespread attention as an alternative to traditional fossil energy. Platinum (Pt) catalytic hydrogen evolution reaction (HER) is a promising technology to produce hydrogen because the consumed electricity can be generated from renewable energy. To overcome the high cost of Pt, one effective strategy is decreasing the Pt nanoparticle (NP) size from submicron to nano-scale or even down to single atom level for efficient interacting water molecules. Herein, atomically dispersed Pt and ultra-fine Pt NPs embedded porous carbons were prepared through the pyrolysis of Pt porphyrin-based conjugated microporous polymer. As-prepared electrocatalyst exhibit high HER activity with overpotential of down to 31 mV at 10 mA cm^-2, and mass activity of up to 1.3 A mg_Pt^-1 at overpotential of 100 mV, which is double of commercial Pt/C (0.66 A mg_Pt^-1). Such promising performance can be ascribed to the synergistic effect of the atomically dispersed Pt and ultra-fine Pt NPs. This work provides a new strategy to prepare porous carbons with both atomically dispersed metal active sites and corresponding metal NPs for various electrocatalysis, such as oxygen reduction reaction, carbon dioxide reduction, etc.

Copper-induced synthesis of palladium/copper popcorn nanoparticles as sensors for differential pulse voltammetric determination of dopamine

Popcorn nanoparticles (pop-NPs) consisting of a Pd/Cu alloy were synthesized using a seed-mediated growth method. The Cu and Pd atoms were co-deposited on a cubic Pd seed to reduce the energy of fault stacking. The same synthesis method with a reduced volume of the Cu(II) salt leads to Pd/Cu alloy nanoparticles with branches (br-NPs). Large Pd nanocubes (Pd NCs) were prepared via epitaxial deposition and using tetrachloropalladate (PdCl₄^2-) only. The high-resolution TEM analysis results show the pop-NPs and br-NPs to be single crystals with [Formula: see text] and [Formula: see text] planes, respectively. The results of X-ray photoelectron spectroscopy and cyclic voltammetry measurements corroborated that Pd is enriched on both surfaces. The materials were placed on a glassy carbon electrode to obtain a differential pulse voltammetric sensor for dopamine (DA). The electrochemical sensitivities are (a) 1.55 μA μM^-1 cm^-2 for the Pd/Cu pop-NP sensor in its linear range (15-300 μM), (b) 1.17 μA μM^-1 cm^-2 for the br-NP sensor in the linear range (15-200 μM), and (c) 0.97 μA μM^-1 cm^-2 for the Pd NC sensor in its linear range (15-100 μM). The best working potentials are near 0.10 V (vs. SCE) for all three sensors. The pop-NP-based sensor performs particularly well due to it selectivity over ascorbic and uric acid. Graphical abstract Pd/Cu popcorn nanoparticles (pop-NPs), nanoparticles with branches (br-NPs), and Pd nanocubes (NCs) were synthesized using seed-mediated growth methods and directly used on glassy carbon electrodes for non-enzymatic sensing of dopamine.