Dendrite-like PtAg alloyed nanocrystals: Highly active and durable advanced electrocatalysts for oxygen reduction and ethylene glycol oxidation reactions

Unique (100) Surface Configuration Enables Promising Oxygen Reduction Performance for Pt3Co Nanodendrite Catalysts

Selective exposure of active surfaces of Pt-based electrocatalysts has been demonstrated as an effective strategy to improve Pt utilization and promote oxygen reduction reaction (ORR) activity in fuel cell application. However, challenges remain in stabilizing those active surface structures, which often suffer undesirable degradation and poor durability along with surface passivation, metal dissolution, and agglomeration of Pt-based electrocatalysts. To overcome the aforementioned obstacles, we here demonstrate the unique (100) surface configuration enabling active and stable ORR performance for bimetallic Pt₃Co nanodendrite structures. Using elaborate microscopy and spectroscopy characterization, it is revealed that the Co atoms are preferentially segregated and oxidized at the Pt₃Co(100) surface. In situ X-ray absorption spectroscopy (XAS) shows that such (100) surface configuration prevents the oxygen chemisorption and oxide formation on active Pt during the ORR process. Thus, the Pt₃Co nanodendrite catalyst shows not only a high ORR mass activity of 730 mA/mg at 0.9 V vs RHE, which is 6.6-fold higher than that of the Pt/C, but also impressively high stability with 98% current retention after the acceleration degradation test in acid media for 5000 cycles, far exceeding the Pt or Pt₃Co nanoparticles. Density functional theory (DFT) calculation also confirms the lateral and structural effects from the segregated Co and oxides on the Pt₃Co(100) surface in reducing the catalyst oxophilicity and the free energy for the formation of an OH intermediate in the ORR.

Simple Synthesis of PdAg Porous Nanowires as Effective Catalysts for Polyol Oxidation Reaction

The development of efficient and stable Pd-based electrocatalysts is extremely important to facilitate the development of catalysts for polyol oxidation reactions. To synthesize Pd-based catalysts with excellent catalytic performance, a series of PdAg porous nanowires (PdAg PNWs) with different elemental ratios was constructed by facile synthesis using a seed-mediated method. The synthesized PdAg PNWs have a rough surface and a porous one-dimensional structure, which optimize the specific surface area and surface area of catalysts, thereby providing more active sites for catalysts. PdAg PNWs benefited from the geometric effect of porous nanowires and the synergy between Pd and Ag, showing excellent catalysis (8243.0 and 4137.0 mA mg_Pd^-1) for the ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR). Among them, the optimal Pd₆₂Ag₃₈ PNWs show the highest catalytic activity (6.0 times and 3.9 times higher than Pd/C) and stability compared with Pd₅₇Ag₄₃ PNWs, Pd₅₁Ag₄₉ PNWs, and Pd/C for EGOR and GOR. At the same time, this porous one-dimensional structure also endows PdAg PNWs with faster electron transfer capabilities than Pd/C. This work will likely provide an effective strategy for constructing cost-effective catalysts.

Recent advances in fuel cell reaction electrocatalysis based on porous noble metal nanocatalysts

As the center of fuel cells, electrocatalysts play a crucial role in determining the conversion efficiency from chemical energy to electrical energy. Therefore, the development of advanced electrocatalysts with both high activity and stability is significant but challenging. Active site, mass transport, and charge transfer are three central factors influencing the catalytic performance of electrocatalysts. Endowed with rich available surface active sites, facilitated electron transfer and mass diffusion channels, and highly active components, porous noble metal nanomaterials are widely considered as promising electrocatalysts toward fuel cell-related reactions. The past decade has witnessed great achievements in the design and fabrication of advanced porous noble metal nanocatalysts in the field of electrocatalytic fuel oxidation reaction (FOR) and oxygen reduction reaction (ORR). Herein, the recent research advances regarding porous noble metal nanocatalysts for fuel cell-related reactions are reviewed. In the discussions, the inherent structural features of porous noble metal nanostructures for electrocatalytic reactions, advanced synthetic strategies for the fabrication of porous noble metal nanostructures, and the structure-performance relationships are also provided.

Core@shell PtAuAg@PtAg Hollow Nanodendrites as Effective Electrocatalysts for Methanol and Ethylene Glycol Oxidation

Pt-based catalysts with core@shell structures are widely used in alcohol oxidations due to their excellent catalytic performance. In this work, we synthesized a series of core@shell PtAuAg@PtAg hollow nanodendrites (HNDs) with different compositions by a simple seed-mediated method. The PtAuAg@PtAg HNDs with a hollow core and dendritic shell exhibit excellent catalytic performance for ethylene glycol oxidation reaction (EGOR) and methanol oxidation reaction (MOR). Among these, Pt₃₈Au₂₉Ag₃₃ HNDs have the highest mass activity (12364.0 mA mg_Pt^-1/3278.0 mA mg_Pt^-1) for EGOR and MOR, which is 4.2 times and 5.3 times higher than that of commercial Pt/C (2941.0 mA mg_Pt^-1/617.6 mA mg_Pt^-1), respectively. More importantly, after successive cyclic voltammetry tests, the retained mass activities of Pt₃₈Au₂₉Ag₃₃ HNDs are 3913.8 mA mg_Pt^-1 and 348.3 mA mg_Pt^-1, which are much higher than that of commercial Pt/C as well. The excellent catalytic performance of PtAuAg@PtAg HNDs can be attributed to the structure of HNDs, which can greatly increase the surface area and active sites, as well as the electronic and synergistic effects among Pt, Au, and Ag. This research may provide new ideas for the development of high-efficiency hollow catalytic materials for EGOR and MOR.

Surface Plasmon Resonance Boost Electrocatalytic Alcohol Oxidation over Three-Dimensional PdM (M = Au, Ag, Cu) Nanosheet Assemblies

Photoelectrocatalytic nanomaterials are promising for direct alcohol fuel cells, but the construction of high-efficiency catalysts remains difficult. We herein successfully synthesized three-dimensional (3D) PdM nanosheet assemblies (PdM NSAs, M = Au, Ag, and Cu) through a seed-mediated growth method, which displayed a typical 3D nanoflower morphology assembled from many two-dimensional ultrathin nanosheets. Due to the open 3D structure and the synergistic and electronic effects between Pd and Ag, the optimized PdAg NSAs showed the highest mass activity (9378 mA mg^-1) for the ethylene glycol oxidation reaction. More interestingly, when irradiated with visible light, the mass activity increased to 14 590 mA mg^-1, 12.1 times higher than that of the commercial Pd/C (1205 mA mg^-1). In addition, the as-obtained catalysts also showed better long-term durability than that of the commercial Pd/C under the condition of with or without visible-light illumination. This work highlights the utilization of light energy in designing excellent photoelectrocatalysts to promote the photoelectrocatalytic performance of anode catalysts for fuel cells.

Effect of Anode Material on Electrochemical Oxidation of Low Molecular Weight Alcohols-A Review

The growing climate crisis inspires one of the greatest challenges of the 21st century-developing novel power sources. One of the concepts that offer clean, non-fossil electricity production is fuel cells, especially when the role of fuel is played by simple organic molecules, such as low molecular weight alcohols. The greatest drawback of this technology is the lack of electrocatalytic materials that would enhance reaction kinetics and good stability under process conditions. Currently, electrodes for direct alcohol fuel cells (DAFCs) are mainly based on platinum, which not only provides a poor reaction rate but also readily deactivates because of poisoning by reaction products. Because of these disadvantages, many researchers have focused on developing novel electrode materials with electrocatalytic properties towards the oxidation of simple alcohols, such as methanol, ethanol, ethylene glycol or propanol. This paper presents the development of electrode materials and addresses future challenges that still need to be overcome before direct alcohol fuel cells can be commercialized.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

Tunable long-chains of core@shell PdAg@Pd as high-performance catalysts for ethanol oxidation

High performance nanomaterial catalysts have attracted great attention on the application for the direct alcohol fuel cell. To improve the catalytic behavior, it is a challenge to modulate the surface structure and morphology of catalysts. We integrated properties of advanced networks nanostructure and core@shell structure to form a series of PdAg@Pd worm-like networks catalysts. Importantly, the composition-optimized Pd₇₆Ag₂₄ WNWs exhibited excellent catalytic performance towards ethanol oxidation reaction compared to that of commercial Pd/C catalysts in alkaline media. The mass activity of Pd₇₆Ag₂₄ WNWs is 3.55 times higher than that of commercial Pd/C catalysts for EOR. Moreover, the Pd₇₆Ag₂₄ WNWs also showed superior stability after 250 successive cycles and kept far higher residual activities than that of the other catalysts. The synthesis of PdAg@Pd worm-like networks catalysts provides a reference to well combine the advantages of core@shell and networks structure to form high performance catalysts application for DEFC.

Segmentation and Re-encapsulation of Porous PtCu Nanoparticles by Generated Carbon Shell for Enhanced Ethylene Glycol Oxidation and Oxygen-Reduction Reaction

Hierarchical porous carbon-encapsulated ultrasmall PtCu (UsPtCu@C) nanoparticles (NPs) were constructed based on segmentation and re-encapsulation of porous PtCu NPs by using glucose as a green biomass carbon source. The synergistic electronic effect from the bimetallic elements can enhance the catalytic activity by adjusting the surface electronic structure of Pt. Most importantly, the generated porous carbon shell provided a large contact surface area, excellent electrical conductivity, and structural stability, and the ultrasmall PtCu NPs exhibited an increased electrochemical performance compared with their PtCu matrix because of the exposure of more catalytically active centers. This synergistic relationship between the components resulted in enhanced catalytic activity and better stability of the obtained UsPtCu@C for ethylene glycol oxidation reaction and the oxygen-reduction reaction in alkaline electrolyte, which was higher than the PtCu NPs and commercial Pt/C (20 wt % Pt on Vulcan XC-72). The electrochemically active surface areas of the UsPtCu@C, PtCu NPs, and commercial Pt/C were calculated to be approximately 230.2, 32.8, and 64.0 m²/g_Pt, respectively; the mass activity of the UsPtCu@C for the ethylene glycol oxidation reaction was 8.5 A/mg_Pt, which was 14.2 and 8.5 times that of PtCu NPs and commercial Pt/C, respectively. The specific activity of UsPtCu@C was 3.7 mA/cm_pt², which was 2.1 and 2.3 times that of PtCu NPs and commercial Pt/C, respectively. The onset potential (E_on-set) of UsPtCu@C for the oxygen-reduction reaction was 0.96 V (vs reversible hydrogen electrode, RHE), which was 110 and 60 mV higher than PtCu and commercial Pt/C, respectively. The half-wave potentials (E_1/2) of UsPtCu@C, PtCu, and Pt/C were 0.88, 0.56, and 0.82 V (vs RHE), respectively, which indicated that the UsPtCu@C catalyst had an excellent bifunctional electrocatalytic activity.

Facile synthesis of clean PtAg dendritic nanostructures with enhanced electrochemical properties

PtAg dendritic nanocrystals were synthesized by a one-step and surfactant-free route and exhibited excellent activities in both MOR and ORR.

Highly efficient ethylene glycol electrocatalytic oxidation based on bimetallic PtNi on 2D molybdenum disulfide/reduced graphene oxide nanosheets

In this paper, a two-dimensional (2D) hybrid material of molybdenum disulfide (MoS₂)/reduced graphene oxide (RGO) is facilely synthesized and used as an ideal support for the deposition of Pt nanoparticles. The as-prepared Pt/MoS₂/RGO composites are further worked as electrocatalysts towards ethylene glycol oxidation reaction (EGOR). In addition, when alloying with Ni, the composite shows obvious enhancement in electrocatalytic performance for EGOR. Specifically, the optimized molar ratio of Pt to Ni is 3:1, namely Pt₃Ni/MoS₂/RGO performs the strongest current density of 2062 mA mg^-1_Pt, which is 11.1, 5.80 and 2.40 times higher than those of Pt, Pt₃Ni and Pt/MoS₂/RGO electrodes, respectively. The systematically electrochemical measurements indicate that the largely promoted electrocatalytic performances of Pt₃Ni/MoS₂/RGO are mainly attributed to the synergistic effect of Ni and Pt, and 2D sheets of MoS₂/RGO. This excellent performance indicates that the reported electrocatalytic material could be an efficient catalyst for the application in direct ethylene glycol fuel cell and beyond.

One-pot fabrication of Nitrogen-doped graphene supported binary palladium-sliver nanocapsules enable efficient ethylene glycol electrocatalysis

Fuel cells hold great potential of replacing traditional fossil fuel to alleviate the energy crisis and increasing environmental concerns. Although great progresses have been achieved over decades, the sluggish reaction kinetics and poor durability of electrocatalysts in fuel cells have been the decisive bottleneck that limited their practical applications. Herein, we focus on the design and development of cost-efficient anode electrocatalysts for fuel cells and report the successful creation of an advanced class of N-doped graphene (NG) supported binary PdAg nanocapsules (PdAg NCPs). The well-defined nanocatalysts with highly open structure exhibit greatly improved electrocatalytic performances for ethylene glycol oxidation reaction (EGOR). In particular, the optimized PdAg NCPs/NG show the mass and specific activities of 6118.3 mA mg^-1 and 13.8 mA cm^-2, which are 5.8 and 6.9 times larger than those of the commercial Pd/C catalysts, respectively. More importantly, such PdAg NCPs/NG can also maintain at least 500 potential cycles with limited catalytic activity attenuation, showing an advanced class of electrocatalysts for fuel cells.

Hollow Ag44Pt56 nanotube bundles with high electrocatalytic performances for hydrogen evolution and ethylene glycol oxidation reactions

It is a main challenge to synthesize highly efficient and durable nanocatalysts towards hydrogen evolution reaction (HER) and alcohol oxidation reaction in energy conversion and storage. Herein, a green wet-chemical approach was developed to directly prepare hollow Ag₄₄Pt₅₆ nanotube bundles (H-Ag₄₄Pt₅₆ NTBs), utilizing 5-azacytosine as a structure-directing agent. The obtained electrocatalyst displayed superior catalytic activity and durability for HER in acid media, and the great improvement in catalytic performance for ethylene glycol oxidation reaction (EGOR) in the alkaline electrolyte, outperforming home-made Ag₃₄Pt₆₆ nanoparticles (NPs), Ag₇₀Pt₃₀ NPs, and commercial Pt/C catalysts. The high electrocatalytic characters are mainly attributed to the special nanostructures and the synergetic effects between the bimetals.

Dicyandiamide and iron-tannin framework derived nitrogen-doped carbon nanosheets with encapsulated iron carbide nanoparticles as advanced pH-universal oxygen reduction catalysts

The development of an efficient and cost-effective electrocatalyst toward the oxygen reduction reaction (ORR) is of critical importance for diverse renewable electrical energy techniques. Herein, a dicyandiamide and iron-tannin framework-derived nitrogen-doped carbon nanosheet with encapsulated iron carbide nanoparticle (Fe₃C/N-CNS) is developed. Particularly, dicyandiamide is the key to achieve this two-dimensional nitrogen-doped lamellar carbon nanosheet. Owing to the synergistic characteristics including composition and structure, the optimal catalyst exhibits the comparable or even better catalytic activity, as well as superior methanol tolerance and stability compared with platinum/carbon catalyst over the whole pH range. More notably, the current approach can be potentially extended to synthesize additional two-dimensional structured transition-metal/carbon composites for various energy conversion and storage technologies.

Icosahedral Pt-Ni Nanocrystalline Electrocatalyst: Growth Mechanism and Oxygen Reduction Activity

Engineering the structure of Pt alloy offers an effective way to the design of high performance electrocatalysts. Herein, we synthesize a sandwich-structured, icosahedral Pt_2.1 Ni catalyst through a hot injection method. Its growth involves three steps: 1) burst nucleation of Pt atoms to form a Pt-enriched core, 2) heterogeneous nucleation of Ni atoms onto the Pt core to form a Ni-enriched interlayer, and 3) kinetic controlled growth of a Pt-enriched shell. The Pt-enriched core protects the nanostructure from collapse and mitigates the strain change caused by lattice mismatch, and thus enhances the stability of the structure. The Ni-enriched interlayer induces the electronic modification of the outermost Pt shell, and in turn tunes the activity. The Pt-enriched shell provides more active sites through the exposure of (1 1 1) facets and retards the dissolution of Ni atoms. As a result, this sandwich-structure enables impressive electrocatalytic activity (0.91 mA cm^-2 and 0.32 AmgPt-1 @ 0.9 V) and duability.

Particle size effects of PtAg nanoparticles on the catalytic electrooxidation of liquid fuels

The electrocatalytic oxidation of ethylene glycol and glycerol in the presence of PtAg NPs catalyst showed a linear decrease with the increasing particle sizes, providing new clues and hypotheses on how quantum confinement phenomena affect the electrocatalytic performances.

An efficient and cost-effective tri-functional electrocatalyst based on cobalt ferrite embedded nitrogen doped carbon

The development of efficient, cost-effective and long-lived electro-catalyst is necessary for the realization of practically viable water-splitting systems. A trifunctional electrocatalyst for water splitting (hydrogen evolution, oxygen reduction and oxygen evolution reaction, HER/ORR/OER) was designed via eco-friendly and facial way. CoFe₂O₄ nanoparticles embedded in nitrogen doped mesoporous carbon were prepared using chicken egg white/albumin after pyrolysis at different temperatures, 700, 800, 900 and 1000 °C. The specific surface area, pore size and the interaction between CoFe₂O₄ nanoparticles and carbon matrix were tuned via pyrolysis temperature. The catalyst prepared at 900 °C, (N/CF-EC-900) exhibit superior catalytic activity as well as the superior stability than that other nanocomposites prepared and other commercial catalyst (Pt/C, RuO₂) for water splitting. Our findings emphasize the importance of CoFe₂O₄ nanoparticles embedded in the carbon and suggest the catalytic activities with low onset potential, high current densities, small Tafel slope in basic medium.

Facile synthesis of hollow dendritic Ag/Pt alloy nanoparticles for enhanced methanol oxidation efficiency

Hollow dendritic Ag/Pt alloy nanoparticles were synthesized by a double template method.