Deep eutectic solvent-assisted synthesis of highly efficient PtCu alloy nanoclusters on carbon nanotubes for methanol oxidation reaction

Electrocatalysis in deep eutectic solvents: from fundamental properties to applications

Electrocatalysis stands out as a promising avenue for synthesizing high-value products with minimal environmental footprint, aligning with the imperative for sustainable energy solutions. Deep eutectic solvents (DESs), renowned for their eco-friendly, safe, and cost-effective nature, present myriad advantages, including extensive opportunities for material innovation and utilization as reaction media in electrocatalysis. This review initiates with an exposition on the distinctive features of DESs, progressing to explore their applications as solvents in electrocatalyst synthesis and electrocatalysis. Additionally, it offers an insightful analysis of the challenges and prospects inherent in electrocatalysis within DESs. By delving into these aspects comprehensively, this review aims to furnish a nuanced understanding of DESs, thus broadening their horizons in the realm of electrocatalysis and facilitating their expanded application.

Pd Nanoparticle-Decorated Novel Ternary Bi2O2CO3-Bi2MoO6-CuO Heterojunction for Enhanced Photo-electrocatalytic Ethanol Oxidation

Recently, photo-electrooxidation of fuel using a noble metal-semiconductor junction has been one of the most promising approaches in fuel cell systems. Herein, we report the development of a Pd-supported Bi2MoO6-Bi2O2CO3-CuO novel ternary heterojunction for ethanol oxidation in alkali in the presence and absence of visible light. Various spectroscopic and microscopic characterization techniques confirm strong coupling between palladium nanoparticles and Bi2MoO6-Bi2O2CO3-CuO ternary heterojunction supports. The photo-electrocatalytic efficacy of the synthesized catalysts was inspected by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The CV study reveals that the forward peak current density (in mA mg-1 of Pd) of the synthesized quaternary heterojunction was about 1482.5, which is 2.4, 4, and 4.6 times higher than that of Pd/CuO (608.3), Pd/Bi2MoO6-Bi2O2CO3 (368.3), and similarly synthesized Pd catalyst (321.5) under visible light radiation. The best heterojunction catalyst shows 2.21-fold higher peak current density in visible light compared to that in dark. CA study reveals that after operation for 6000 s, the current density of the quaternary electrode is 1.5 and 3.4 times greater than that of Pd/CuO and Pd/C catalysts, respectively. The greater photocurrent response, lower photoluminescence (PL) emission intensity, and smaller semicircle arc in the Nyquist plot of the quaternary catalyst demonstrate the efficient segregation and higher charge transfer conductance of photogenerated charges to facilitate the photo-electrooxidation process of ethanol. The stability test shows that the quaternary catalyst loses only 9.8 and 7.7% of its maximum current density after 500 cycles of CV operation in the dark and light, respectively, indicating that light energy is more beneficial in establishing high stability. The dramatic enhancement of the photo-electrocatalytic activity of the quaternary electrode is owing to the lower band gap, high ECSA, enhanced charge separation of photogenerated carriers (e--h+), and all cocatalytic support of Bi2MoO6, Bi2O2CO3, and CuO in Pd/ Bi2MoO6-Bi2O2CO3-CuO under visible light radiation. The morphology and structure of the used quaternary catalyst are tested using FESEM and PXRD. Finally, ex situ FTIR spectroscopy and HPLC techniques help understand the ethanol electrooxidation reaction mechanism.

Phosphorus-Doped directly interconnected networks of amorphous Metal-Organic framework nanowires for efficient methanol oxidation

Developing high-performance and low-cost electrocatalysts toward methanol oxidation reaction (MOR) is essential for fuel cell applications. Herein, we report a defect engineering strategy integrating amorphization and phosphorization to construct directly interconnected networks of amorphous NiCo-based metal-organic framework nanowires (a-NiCo-MOFNWs) with phosphorus (P) doping. The resulting P-doped a-NiCo-MOFNWs (a-NiCo-MOFNWs-P) network displays superior MOR efficiency and long-term durability over 1000 cyclic voltammetry (CV) measurements. The special structure of directly interconnected networks and the synergistic effect between the amorphous MOFs and dispersed phosphorus species give rise to abundant exposed active sites, accelerated electron transport, and increased porosity for mass transfer, thus boosting the reaction kinetics of MOR. This work provides additional insights into the network assembly and structural evolution of one-dimensional (1D) MOFs, and also opens up new avenues for the design of highly reactive and robust non-precious metal-based electrocatalysts.

A high-performance Pt-based catalyst for the methanol oxidation reaction: effect of electrodeposition mode and cocatalyst on electrocatalytic activity

The influence of supporting material, cocatalyst, and electrodeposition mode on MOR activity.

Pd3Co1 Alloy Nanocluster on the MWCNT Catalyst for Efficient Formic Acid Electro-Oxidation

In this study, the Pd₃Co₁ alloy nanocluster from a multiwalled carbon nanotube (MWCTN) catalyst was fabricated in deep eutectic solvents (DESs) (referred to Pd₃Co₁/CNTs). The catalyst shows a better mass activity towards the formic acid oxidation reaction (FAOR) (2410.1 mA mg_Pd^-1), a better anti-CO toxicity (0.36 V) than Pd/CNTs and commercial Pd/C. The improved performance of Pd₃Co₁/CNTs is attributed to appropriate Co doping, which changed the electronic state around the Pd atom, lowered the d-band of Pd, formed a new Pd-Co bond act at the active sites, affected the adsorption of the toxic intermediates and weakened the dissolution of Pd; moreover, with the assistance of DES, the obtained ultrafine Pd₃Co₁ nanoalloy exposes more active sites to enhance the dehydrogenation process of the FAOR. The study shows a new way to construct a high-performance Pd-alloy catalyst for the direct formic acid fuel cell.

PtCuFe alloy nanochains: Synthesis and composition-performance relationship in methanol oxidation and hydrogen evolution reactions

The controllable synthesis of 1-dimensional (1D) multi-metal Pt-based alloys, with enhanced electro-chemical properties remains a challenge, despite the wide application of Pt-based catalysts in fuel cells and in the hydrogen evolution reaction (HER). Herein, we fabricate PtCuFe alloy nanochains (NCs) that have a tunable composition by flexibly adjusting the molar ratios of the metal precursors. It was found that Cu²⁺ is key in the formation of 1D NCs, as confirmed by transmission electron microscopy characterizations. In addition, the alloyed Fe can further increase the content of the metallic state of Cu in the PtCuFe NCs. The as-prepared PtCuFe NCs exhibited higher catalytic activity and stability than those of the Pt nanoparticles (NPs), PtFe NPs, and PtCu NCs, for the methanol oxidation reaction (MOR) and HER. Additionally, the composition-performance relationship of PtCu_xFe_y NCs toward the MOR and HER were investigated. The hybrid density functional theory calculation and analysis showed that the 1D PtCuFe NCs have a lower lowest unoccupied molecular orbital (LUMO) than those of the 2- and 3-dimensional PtCuFe, verifying that the 1D PtCuFe NCs exhibit the highest activity for the MOR. This work has established a new method for the controllable synthesis of multi-metal Pt-based NCs/alloy catalysts and their subsequent applications in other electro-catalytic reactions.

Engineering PtCu nanoparticles for a highly efficient methanol electro-oxidation reaction

Achieving a highly efficient and durable methanol electro-oxidation catalyst in acid media is critical for the practical utilization of direct methanol fuel cells (DMFCs) at the commercial scale. Herein, we report a facile and effective one-pot strategy for the synthesis of carbon-supported PtCu alloy nanoparticles (PtCu NPs) with a Pt-rich surface, small particle size and uniform dispersion. The as-prepared PtCu NPs with the optimal alloy composition (Pt₂Cu) exhibit a significantly improved electrochemical methanol oxidation reaction performance in terms of a high activity, superior CO tolerance and remarkable durability, in contrast to those of commercial Pt/C catalysts in acid media. Particularly, the Pt₂Cu/C catalyst exerts a 4.5 times enhancement in the mass activity and a larger I_f/I_b value compared to those of commercial Pt/C (Pt/C_comm). The enhanced catalytic activities can be ascribed to the high utilization of Pt and the high index facets of the surface. Also, the addition of Cu downshifts the d-band center of Pt and improves the CO tolerance during the methanol oxidation reaction process. This work provides an efficient strategy for designing desired Pt-based alloys for various catalytic reactions.

Pt-based (Zn, Cu) nanodendrites with enhanced catalytic efficiency and durability toward methanol electro-oxidation via trace Ir-doping engineering

Pt-based alloy nanomaterials with nanodendrites (NDs) structures are efficient electrocatalysts for methanol oxidation reaction (MOR), however their durability is greatly limited by the issue of transition metals dissolution. In this work, a facile trace Ir-doping strategy was proposed to fabricate Ir-PtZn and Ir-PtCu alloy NDs catalysts in aqueous medium, which significantly improved the electrocatalytic activity and durability for MOR. The as-prepared Ir-PtZn/Cu NDs catalysts showed distinct dendrites structures with the averaged diameter of 4.1 nm, and trace Ir doping subsequently improved the utilization of Pt atoms and promoted the oxidation efficiency of methanol. The electrochemical characterizations further demonstrated that the obtained Ir-PtZn/Cu NDs possessed enhanced mass activities of nearly 1.23 and 1.28-fold higher than those of undoped PtZn and PtCu, and approximately 2.35 and 2.67-fold higher than that of Pt/C in acid medium. More excitingly, after long-term durability test, the proposed Ir-PtZn and Ir-PtCu NDs still retained about 88.9% and 91.6% of its initial mass activities, which further highlights the key role of Ir-doping in determining catalyst performance. This work suggests that trace Ir-doping engineering could be a promising way to develop advanced electrocatalysts toward MOR for direct methanol fuel cell (DMFC) applications.

Zinc-Coordination Polymer-Derived Porous Carbon-Supported Stable PtM Electrocatalysts for Methanol Oxidation Reaction

Porous carbon (PC) is obtained by carbonizing a zinc-coordination polymer (MOF-5) at 950 °C and PtM (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs), which are deposited on PC using the polyol method. Structural and morphological characterizations of the synthesized materials are carried out by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), and the porosity was determined using a N2 adsorption/desorption technique. The results revealed that PtM NPs are alloyed in the fcc phase and are well dispersed on the surface of PC. The electrochemical results show that PtM/PC 950 catalysts have higher methanol oxidation reaction (MOR) performances than commercial Pt/C (20%) catalysts. After 3000 s of chronoamperometry (CA) test, the MOR performances decreased in the order of Pt1Cu1/PC 950 > Pt1Ni1/PC 950 > Pt1Fe1/PC 950 > Pt1Zn1/PC 950 > Pt1Co1/PC 950. The high MOR activities of the synthesized catalysts are attributed to the effect of M on methanol dissociative chemisorption and improved tolerance of Pt against CO poisoning. The high specific surface area and porosity of the carbon support have an additional effect in boosting the MOR activities. Screening of the first row transition metals (d 5+n , n = 1, 2, 3, 4, 5) alloyed with Pt binary catalysts for MOR shows that Pt with d 8 (Ni) and d 9 (Cu) transition metals, in equivalent atomic ratios, are good anode catalysts for alcohol fuel cells.

Three-step method with self-sacrificial Co to prepare a uniform 5 nm-scale Pt catalyst for the oxygen reduction reaction

Simple and rapid preparation method for a highly dispersed and small-sized CoPt catalyst.

PtPdCu cubic nanoframes as electrocatalysts for methanol oxidation reaction

PtPdCu cubic nanoframes with unique open architecture exhibit excellent electrocatalytic performances toward methanol electrooxidation.

Comparison of electrocatalytic activity of Pt1-x Pd x /C catalysts for ethanol electro-oxidation in acidic and alkaline media

In this paper, a comparision of Pt1-x Pd x /C catalysts for ethanol-oxidation in acidic and alkaline media has been investigated. We prepared Pt1-x Pd x /C catalysts with different ratios of Pt/Pd (x at% = 0, 27, 53, 77 and 100) by the formic acid reduction method. The obtained Pt1-x Pd x /C catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), induced coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Structural and morphological investigations of the as-prepared catalysts revealed that the metallic particle size increases with increasing Pd content in the catalyst. The electrocatalytic performances and stabilities of Pt1-x Pd x /C catalysts were tested by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) measurements for ethanol oxidation in acidic and alkaline media. The electrochemical measurements demonstrate that Pt1-x Pd x /C catalysts exhibit much higher electrocatalytic activity for alcohol oxidation in alkaline media than that in acidic media. The composition of Pt/Pd has a significant impact on the ethanol-oxidation in both acidic and alkaline media. The Pt23Pd77/C catalyst shows the highest electrocatalytic performance with a mass specific peak current of 2453.7 mA mgPtPd -1 in alkaline media, which is higher than the Pt77Pd23/C with the maximum of peak current of 339.7 mA mgPtPd -1 in acidic media. Meanwhile, the effect of electrolyte, CH3CH2OH concentrations and scan rates was also studied for ethanol-oxidation in acidic and alkaline media.