Facile one-pot surfactant-free synthesis of uniform Pd6Co nanocrystals on 3D graphene as an efficient electrocatalyst toward formic acid oxidation

Advancements in Noble Metal-Decorated Porous Carbon Nanoarchitectures: Key Catalysts for Direct Liquid Fuel Cells

Noble-metal nanocrystals have emerged as essential electrode materials for catalytic oxidation of organic small molecule fuels in direct liquid fuel cells (DLFCs). However, for large-scale commercialization of DLFCs, adopting cost-effective techniques and optimizing their structures using advanced matrices are crucial. Notably, noble metal-decorated porous carbon nanoarchitectures exhibit exceptional electrocatalytic performances owing to their three-dimensional cross-linked porous networks, large accessible surface areas, homogeneous dispersion (of noble metals), reliable structural stability, and outstanding electrical conductivity. Consequently, they can be utilized to develop next-generation anode catalysts for DLFCs. Considering the recent expeditious advancements in this field, this comprehensive review provides an overview of the current progress in noble metal-decorated porous carbon nanoarchitectures. This paper meticulously outlines the associated synthetic strategies, precise microstructure regulation techniques, and their application in electrooxidation of small organic molecules. Furthermore, the review highlights the research challenges and future opportunities in this prospective research field, offering valuable insights for both researchers and industry experts.

Ultrafast synthesis of efficient TS-PtCoCu/CNTs composite with high feed-to-product conversion rate by Joule heating for electrocatalytic oxidation of ethanol

Due to the challenges involved in achieving high metal load, uniform metal dispersion and nanosized metal particles simultaneously, it is difficult to develop a simple protocol for the rapid and efficient synthesis of Pt-based composites for electrocatalytic ethanol oxidation reaction (EOR). In this study, a facile ultrafast thermal shock strategy via Joule heating was applied to fabricate a series of PtCoCu ternary nanoalloys decorated carbon nanotube composites (TS-PtCoCu/CNTs), without the need for a reducing agent or surfactant. The TS-PtCoCu/CNTs with optimal Pt content (∼15 %) exhibited excellent EOR activity, with mass and specific activity of 3.58 A mgPt-1 and 5.79 mA cm-2, respectively, which are 3.8 and 13.5 times higher than those of Pt/C. Compared with the control prepared through the traditional furnace annealing, the catalyst also showed excellent activity and stability. DFT calculations revealed that the TS-PtCoCu/CNTs possesses a downshifted d-band center, weakened CO adsorption and higher OH affinity compared with monometallic Pt, all of which lead to the preferred C1 pathway for EOR. This study demonstrates an ultrafast construction of a highly efficient Pt-Co-Cu ternary catalyst for EOR. Additionally, it provides insights into the reaction mechanism based on structural characterization, electrochemical characterization, and theoretical calculations.

Sn-doped PdCu alloy nanosheet assemblies as an efficient electrocatalyst for formic acid oxidation

A ternary alloy catalyst has been confirmed to be an effective catalyst for anode catalysis in direct formic acid fuel cells, which can improve the electrocatalytic performance of the fuel cell by introducing commonly used metal elements to change the Pd electronic structure and can reduce the use of precious metals and the cost of catalyst production. In this study, PdCuSn Ns/C with a special 3D structure was synthesized by a simple two-step wet chemical method. The PdCuSn Ns/C catalyst prepared exhibits excellent catalytic activity and stability for the formic acid oxidation reaction (FAOR). The mass activity of 2420.1 mA mg-1Pd is 3.94 times that of the Pd/C catalyst. The improvement in the electrocatalytic performance stems from the introduction of Cu and Sn atoms and the unique 3D nanosheet structure, which changes the electronic structure of Pd to increase the reactive active site and accelerates the reaction mass transfer rate, and also reduces the content of precious metals, while improving the electrocatalytic performance. Therefore, the PdCuSn Ns/C catalyst has a promising future in the field of electrocatalysis.

A "Special" Solvent to Prepare Alloyed Pd2Ni1 Nanoclusters on a MWCNT Catalyst for Enhanced Electrocatalytic Oxidation of Formic Acid

Herein, an electrocatalyst with Pd₂Ni₁ nanoclusters, supporting multiwalled carbon nanotubes (MWCNTs) (referred to Pd₂Ni₁/CNTs), was fabricated with deep eutectic solvents (DES), which simultaneously served as reducing agent, dispersant, and solvent. The mass activity of the catalyst for formic acid oxidation reaction (FAOR) was increased nearly four times compared to a Pd/C catalyst. The excellent catalytic activity of Pd₂Ni₁/CNTs was ascribed to the special nanocluster structure and appropriate Ni doping, which changed the electron configuration of Pd to reduce the d-band and to produce a Pd-Ni bond as a new active sites. These newly added Ni sites obtained more OH^- to release more effective active sites by interacting with the intermediate produced in the first step of FAOR. Hence, this study provides a new method for preparing a Pd-Ni catalyst with high catalytic performance.

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.

Engineering the morphology of palladium nanostructures to tune their electrocatalytic activity in formic acid oxidation reactions

Pd nanomaterials can be cheaper alternative catalysts for the electrocatalytic formic acid oxidation reaction (FAOR) in fuel cells. The size and shape of the nanoparticles and crystal engineering can play a crucial role in enhancing the catalytic activities of Pd nanostructures. A systematic study on the effect of varying the morphology of Pd nanostructures on their catalytic activities for FAOR is reported here. Palladium nanoparticles (Pd_0D), nanowires (Pd_1D) and nanosheets (Pd_2D) could be synthesized by using swollen liquid crystals as 'soft' templates. Swollen liquid crystals are lyotropic liquid crystals that are formed from a quaternary mixture of a surfactant, cosurfactant, brine and Pd salt dissolved in oil. Pd_1D nanostructures exhibited 2.7 and 19 fold higher current density than Pd_0D and Pd_2D nanostructures in the FAOR. The Pd_1D nanostructure possess higher electrochemically active surface area (ECSA), better catalytic activity, stability, and lower impedance to charge transfer when compared to the Pd_0D and Pd_2D nanostructures. The presence of relatively higher amounts of crystal defects and enriched (100) crystal facets in the Pd_1D nanostructure were found to be the reasons for their enhanced catalytic activities.

Anchoring nanosized Pd on three-dimensional boron- and nitrogen-codoped graphene aerogels as a highly active multifunctional electrocatalyst for formic acid and methanol oxidation reactions

A facile and scalable strategy is developed for the preparation of nanosized Pd crystals anchored on 3D B- and N-codoped graphene aerogels, which show multifunctional electrocatalytic ability.

Polymer fiber membrane-based direct ethanol fuel cell with Ni-doped SnO2 promoted Pd/C catalyst

The PFM-based DEFC with as-prepared Pd/Ni–SnO₂/C as the anode catalyst and porous NiCo₂O₄ as the cathode catalyst delivers encouraging properties.

Highly Active and Durable Ultrasmall Pd Nanocatalyst Encapsulated in Ultrathin Silica Layers by Selective Deposition for Formic Acid Oxidation

The low performance of palladium (Pd) is a considerable challenge for direct formic acid fuel cells in practical applications. Herein, we develop a simple strategy to synthesize a highly active and durable Pd nanocatalyst encapsulated in ultrathin silica layers with vertically aligned nanochannels covered graphene oxides (Pd/rGO@pSiO₂) without blocking active sites by selective deposition. The Pd/rGO@pSiO₂ catalyst exhibits very high performance for a formic acid oxidation (FAO) reaction compared with the Pd/rGO without protective silica layers and commercial Pd/C catalysts. Pd/rGO@pSiO₂ shows an FAO activity 3.9 and 3.8 times better than those of Pd/rGO and Pd/C catalysts, respectively. The Pd/rGO@pSiO₂ catalysts are also almost 6-fold more stable than Pd/C and more than 3-fold more stable than Pd/rGO. The outstanding performance of our encapsulated Pd catalysts can be ascribed to the novel design of nanostructures by selective deposition fabricating ultrasmall Pd nanoparticles encapsulated in ultrathin silica layers with vertically aligned nanochannels, which not only avoid blocking the active sites but also facilitate the mass transfer in encapsulated catalysts. Our work indicates an important method to the rational design of high-performance catalysts for fuel cells in practical applications.

An environmentally friendly one-pot synthesis method by the ultrasound assistance for the decoration of ultrasmall Pd-Ag NPs on graphene as high active anode catalyst towards ethanol oxidation

An environmentally friendly one-pot synthesis approach for the decoration of Pd-Ag nanoparticles with the ultrasmall size on graphene (Pd-Ag/G) by the assistance of ultrasound is proposed in this paper. This method offers exceptional advantages over other approaches such as environmentally friendly synthesis, being low temperature, reductant, surfactant free, simple, fast and one-pot synthesis. In this work, silver formate is added to the graphene suspension at 25 °C. Then, PdCl₂ is added to the suspension under stirring to fabricate Pd-Ag/G. The uniform dispersity of nanoparticles with an average size of about 2-3 nm is well confirmed by transmission electron microscopy micrographs. The resultant catalyst is applied as anode electrocatalyst towards electrooxidation reaction of ethanol. The Pd-Ag/G catalyst displays exceptional catalytic activity and durability towards electro-oxidation of ethanol. According to the obtained results, it be concluded that the combination of Ag and Pd, ultrasmall and uniform distribution of Pd-Ag nanoparticles led to the improvement of electrocatalytic activity of the Pd-Ag/G catalyst.

Cyanogel auto-reduction induced synthesis of PdCo nanocubes on carbon nanobowls: a highly active electrocatalyst for ethanol electrooxidation

Direct ethanol fuel cells (DEFCs) with a high conversion efficiency are quite promising candidates for energy conversion devices. Herein, we have successfully synthesized PdCo alloy nanocubes supported on carbon nanobowl (denoted as Pd₂Co₁/CNB) nanohybrids by using the cyanogel auto-reduction method at high temperature. The morphology, composition and structure of Pd₂Co₁/CNB nanohybrids are characterized in detail, revealing that PdCo nanocubes have a high alloying degree and special {110} facets. In cyclic voltammetry measurements, Pd₂Co₁/CNB nanohybrids show a mass activity of 1089.0 A g _Pd^-1 and a specific activity of 40.03 mA cm^-2 for ethanol electrooxidation at peak potential, which are much higher than that of the commercial Pd/C electrocatalyst (278.2 A g_Pd^-1 and 8.22 mA cm^-2). Additionally, chronoamperometry measurements show that Pd₂Co₁/CNB nanohybrids have excellent durability for ethanol electrooxidation. A high alloying degree, special {110} facets and the CNB supporting material contribute to the high activity and durability of Pd₂Co₁/CNB nanohybrids, making them a highly promising Pt-alternative electrocatalyst for ethanol electrooxidation in DEFCs.

Pt Nanoparticle-Loaded Graphene Aerogel Microspheres with Excellent Methanol Electro-Oxidation Performance

Platinum-decorated graphene aerogel microspheres were fabricated through a combined electrospraying, freeze-casting, and solvothermal process. Platinum nanoparticles with a narrow size distribution are evenly anchored on the graphene aerogel microspheres without agglomeration benefitting from the distinct center-diverging microchannel structure of the graphene aerogel microspheres, which results in the as-prepared catalysts presenting excellent electrocatalytic performance including high electrocatalytic activity and high poison tolerance toward methanol electro-oxidation, showing great potential for direct methanol fuel cell anode catalysts. In particular, the platinum-decorated graphene aerogel microspheres exhibit an extremely high mass activity of 1098.9 mA mg^-1 toward methanol oxidation as well as excellent antipoisoning ability, which are dramatically enhanced compared with Pt particles dispersed on graphene oxide and commercial carbon black supports.

Ir-Alloyed Ultrathin Ternary PdIrCu Nanosheet-Constructed Flower with Greatly Enhanced Catalytic Performance toward Formic Acid Electrooxidation

Ternary metal-element alloys have been reported as efficient electrocatalysts toward various electrochemical reactions, but a unique three-dimensional (3D) Ir-alloyed ternary nanosheet-composed flower (NCF) structure has not been explored yet. Herein, an innovated 1.8 nm Ir-alloyed ultrathin ternary PdIrCu NCF structure is synthesized via one-pot solvothermal reduction without using any surfactant. The as-prepared PdIrCu/C NCF catalyst remarkably improves the stability than commercial Pd/C toward formic acid electrooxidation while resulting in significantly increased mass activity. The improvement of electrocatalytic properties depends on the introduction of Ir and Cu atoms, which greatly prevented poisoning from CO while modifying the electronic structure of Pd for increased reaction active sites and accelerated charge-transfer rate as well as facilitated mass transport by ultrathin NCF 3D structure. Therefore, this catalyst possesses a promising application prospect in electrochemical energy storage/conversion systems.

Silsesquioxane stabilized platinum-palladium alloy nanoparticles with morphology evolution and enhanced electrocatalytic oxidation of formic acid

Bimetallic catalysts have attracted enormous attention with their enhanced electrocatalytic properties in fuel cells. Herein a series of silsesquioxane (POSS) stabilized platinum-palladium (PtPd) alloy nanoparticles (NPs) with morphology evolution were facilely synthesized with the co-chemical reduction using formaldehyde as the reductant. By varying the ratio of Pt to Pd, the PtPd alloy NPs evolved from truncated octahedrons to octahedrons, and triangular nanoplates. The mechanism of morphology evolution is that Pt and Pd could self-assemble on POSS to form Pt_xPd_1-x intermediates with different Pt/Pd ratios. In addition, formaldehyde could selectively bind to the {1 1 1} facets of Pd to control the growth rates of different facets and help Pt_xPd_1-x intermediates with different Pt/Pd ratio grow into different morphology of Pt_xPd_1-x alloys. The morphology tuning endowed the PtPd alloy NPs superior performance for formic acid electrooxidation. Compared with Pt, Pd NPs, and commercial Pt/C catalyst, the PtPd alloy NPs displayed larger electrochemically active surface area, enhanced electrocatalytic activity and durability toward oxidation of formic acid, and increased CO tolerance. This work suggested that modification of catalytic activity through morphology tuning with composition adjustment might provide some new pathways for the design of promising catalysts with advanced performance.

Center-iodized graphene as an advanced anode material to significantly boost the performance of lithium-ion batteries

Iodine edge-doped graphene can improve the capacity and stability of lithium-ion batteries (LIBs). Our theoretical calculations indicate that center-iodization can further significantly enhance the anode catalytic process. To experimentally prove the theoretical prediction, iodine-doped graphene materials were prepared by one-pot hydrothermal and ball-milling approaches to realize different doping-sites. Results show that the center-iodinated graphene (CIG) anode exhibits a remarkably high reversible capacity (1121 mA h g-1 after 180 cycles at 0.5 A g-1), long-cycle life (0.01% decay per cycle over 300 cycles at 1 A g-1) and high-rate capacity (374 mA h g-1 after 800 cycles at 8 A g-1), which greatly improves the performance of the edge-iodinated graphene anode and these results are in good agreement with the theoretical analysis. More importantly, the CIG anode also delivers a high-rate capacity and excellent cycling stability (279 mA h g-1 after 500 cycles at 10 A g-1) in full-cells. Both the theoretical analysis and experimental investigation reveal the enhancement mechanism, in which the center-iodization increases the surface charge for fast electron transfer rate, improves the conductivity for charge transport and rationalizes the pore structure for enhanced mass transport and ion insertion/desertion, thus resulting in a high rate capacity and long cycle life. This work not only discloses the critical role of catalytic sites including both amounts and site positions but also offers great potential for high-power rechargeable LIB applications.

Promotion effect of oxygen-containing functional groups and Fe species on Pd@graphene for CO catalytic oxidation

Catalysts using graphene as a support possessed higher catalytic activity and stability.

Highly poison-resistant Pt nanocrystals on 3D graphene toward efficient methanol oxidation

Highly poison-resistant Pt nanocrystals are synthesized using reductive sugars derived from pectin hydrolysis, showing efficient catalytic performance toward methanol oxidation.