Nanocatalysts for Electrocatalytic Oxidation of Ethanol

Bioinspired graphene-based metal oxide nanocomposites for photocatalytic and electrochemical performances: an updated review

Considering the rapidly increasing population, the development of new resources, skills, and devices that can provide safe potable water and clean energy remains one of the vital research topics for the scientific community. Owing to this, scientific community discovered such material for tackle this issue of environment benign, the new materials with graphene functionalized derivatives show significant advantages for application in multifunctional catalysis and energy storage systems. Herein, we highlight the recent methods reported for the preparation of graphene-based materials by focusing on the following aspects: (i) transformation of graphite/graphite oxide into graphene/graphene oxide via exfoliation and reduction; (ii) bioinspired fabrication or modification of graphene with various metal oxides and its applications in photocatalysis and storage systems. The kinetics of photocatalysis and the effects of different parameters (such as photocatalyst dose and charge-carrier scavengers) for the optimization of the degradation efficiency of organic dyes, phenol compounds, antibiotics, and pharmaceutical drugs are discussed. Further, we present a brief introduction on different graphene-based metal oxides and a systematic survey of the recently published research literature on electrode materials for lithium-ion batteries (LIBs), supercapacitors, and fuel cells. Subsequently, the power density, stability, pseudocapacitance charge/discharge process, capacity and electrochemical reaction mechanisms of intercalation, and conversion- and alloying-type anode materials are summarized in detail. Furthermore, we thoroughly distinguish the intrinsic differences among underpotential deposition, intercalation, and conventional pseudocapacitance of electrode materials. This review offers a meaningful reference for the construction and fabrication of graphene-based metal oxides as effective photocatalysts for photodegradation study and high-performance optimization of anode materials for LIBs, supercapacitors, and fuel cells.

Recent Approaches for Cleaving the C─C Bond During Ethanol Electro-Oxidation Reaction

Direct ethanol fuel cells (DEFCs) play an indispensable role in the cyclic utilization of carbon resources due to its high volumetric energy density, high efficiency, and environmental benign character. However, owing to the chemically stable carbon-carbon (C─C) bond of ethanol, its incomplete electrooxidation at the anode severely inhibits the energy and power density output of DEFCs. The efficiency of C─C bond cleaving on the state-of-the-art Pt or Pd catalysts is reported as low as 7.5%. Recently, tremendous efforts are devoted to this field, and some effective strategies are put forward to facilitate the cleavage of the C─C bond. It is the right time to summarize the major breakthroughs in ethanol electrooxidation reaction. In this review, some optimization strategies including constructing core-shell nanostructure with alloying effect, doping other metal atoms in Pt and Pd catalysts, engineering composite catalyst with interface synergism, introducing cascade catalytic sites, and so on, are systematically summarized. In addition, the catalytic mechanism as well as the correlations between the catalyst structure and catalytic efficiency are further discussed. Finally, the prevailing limitations and feasible improvement directions for ethanol electrooxidation are proposed.

Orbital Occupancy Modulation to Optimize Intermediate Absorption for Efficient Electrocatalysts in Water Electrolysis and Zinc-Ethanol-Air Battery

Spin engineering is a promising way to modulate the interaction between the metal d-orbital and the intermediates and thus enhance the catalytic kinetics. Herein, an innovative strategy is reported to modulate the spin state of Co by regulating its coordinating environment. o-c-CoSe2 -Ni is prepared as pre-catalyst, then in situ electrochemical impedance spectroscopy (EIS) and in situ Raman spectroscopy are employed to prove phase transition, and CoOOH/Co3 O4 is formed on the surface as active sites. In hybrid water electrolysis, the voltage has a negative shift, and in zinc-ethanol-air battery, the charging voltage is lowered and the cycling stability is greatly increased. Coordinated atom substitution and crystalline symmetry change are combined to regulate the absorption ability of reaction intermediates with balanced optimal adsorption. Coordinated atom substitution weakens the adsorption while the crystalline symmetry change strengthens the adsorption. Importantly, the tetrahedral sites are introduced by Ni doping which enables the co-existence of four-coordinated sites and six-coordination sites in o-c-CoSe2 -Ni. The dz2 + dx2 -y2 orbital occupancy decreases after the atomic substitution, while increases after replacing the CoSe6 -Oh field with CoSe6 -Oh /CoSe4 -Td . This work explores a new direction for the preparation of efficient catalysts for water electrolysis and innovative zinc-ethanol-air battery.

Electronic and Geometric Effects Endow PtRh Jagged Nanowires with Superior Ethanol Oxidation Catalysis

Complete ethanol oxidation reaction (EOR) in C1 pathway with 12 transferred electrons is highly desirable yet challenging in direct ethanol fuel cells. Herein, PtRh jagged nanowires synthesized via a simple wet-chemical approach exhibit exceptional EOR mass activity of 1.63 A mgPt-1 and specific activity of 4.07 mA cm-2 , 3.62-fold and 4.28-folds increments relative to Pt/C, respectively. High proportions of 69.33% and 73.42% of initial activity are also retained after chronoamperometric test (80 000 s) and 1500 consecutive potential cycles, respectively. More importantly, it is found that PtRh jagged nanowires possess superb anti-CO poisoning capability. Combining X-ray absorption spectroscopy, X-ray photoelectron spectroscopy as well as density functional theory calculations unveil that the remarkable catalytic activity and CO tolerance stem from both the Rh-induced electronic effect and geometric effect (manifested by shortened Pt─Pt bond length and shrinkage of lattice constants), which facilitates EOR catalysis in C1 pathway and improves reaction kinetics by reducing energy barriers of rate-determining steps (such as *CO → *COOH). The C1 pathway efficiency of PtRh jagged nanowires is further verified by the high intensity of CO2 relative to CH3 COOH/CH3 CHO in infrared reflection absorption spectroscopy.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

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.

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.

Wet-chemistry synthesis of two-dimensional Pt- and Pd-based intermetallic electrocatalysts for fuel cells

Two-dimensional (2D) noble-metal-based nanomaterials have attracted tremendous attention and have widespread promising applications as a result of their unique physical, chemical, and electronic properties. Especially, 2D Pt- and Pd-based intermetallic nanoplates (IMNPs) and nanosheets (IMNSs) are widely studied for fuel cell (FC)-related reactions, including the cathodic oxygen reduction reaction (ORR) and anodic formic acid, methanol and ethanol oxidation reactions (FAOR, MOR and EOR). Wet-chemistry synthesis is a powerful strategy to prepare metallic nanocrystals with well-controlled dispersity, size, and composition. In this review, a fundamental understanding of the FC-related reactions is firstly elaborated. Subsequently, the current wet-chemistry synthesis pathways for 2D Pt- and Pd-based IMNPs and IMNSs are briefly summarized, as well as their electrocatalytic applications including in the ORR, FAOR, MOR, and EOR. Finally, we provide an overview of the opportunities and current challenges and give our perspectives on the development of high-performance 2D Pt- and Pd-based intermetallic electrocatalysts towards FCs. We hope this review offers timely information on the synthesis of 2D Pt- and Pd-based IMNPs and IMNSs and provides guidance for the efficient synthesis and application of them.

Sulfur and phosphorus co-doping optimized electronic structure and modulated intermediate affinity on PdSP metallene for ethanol-assisted energy-saving H2 production

Coupling cathodic hydrogen evolution reaction (HER) and anodic electrochemical oxidation of organic small molecules in a co-electrolysis system could simultaneously realize high-value chemical generation and energy-saving hydrogen production, which, however, require high-performance electrocatalysts. In this work, we developed a one-step solvothermal method to synthesize S, P-co-doped Pd metallene (PdSP metallene) and employed it as a bifunctional electrocatalyst for both the HER and ethanol oxidation reaction (EOR). The co-doping of S and P atoms into Pd metallene could introduce multiple active sites and increase the electrochemically-active surface area. Moreover, the electronic interactions between Pd, S, and P atoms could regulate the electronic structure of the active sites and modulate the intermediate affinity on the resultant PdSP metallene, thus boosting the electrocatalytic HER and EOR performance. In the HER-EOR co-electrolysis system with bifunctional PdSP metallene electrocatalysts, only a 0.88 V of electrolysis voltage was required to fulfill 10 mA cm^-2 current density, much lower than that of pure water electrolysis (1.41 V) using the same electrocatalysts.

Mott Schottky CoSx-MoOx@NF heterojunctions electrode for H2 production and urea-rich wastewater purification

The sluggish kinetics of oxygen evolution reaction (OER) is the bottleneck of alkaline water electrolysis. The urea oxidation reaction (UOR) with much faster kinetics was to replace OER. To further promote UOR, a heterojunction structure assembled of CoS_x and MoO_x was established, and then its superior catalytic activity was predicted by DFT calculation. After that, an ultra-thin CoS_x-MoO_x@nickel foam (CoS_x-MoO_x@NF) electrode with a Mott-Schottky structure was prepared via a facile hydrothermal method, followed by a low-temperature vulcanization. Results highlighted CoS_x-MoO_x@NF electrode presented a superior performance toward UOR, OER, and H₂ evolution reaction (HER). Notably, it exhibited excellent electrocatalytic performance for OER (1.32 V vs. RHE, 10 mA cm^-2), UOR (1.305 V vs. RHE, 10 mA cm^-2), and urea-assisted overall water splitting with a low voltage (1.38 V, 10 mA cm^-2) when CoS_x-MoO_x@NF electrode served as both anode and cathode. It is promising to use CoS_x-MoO_x@NF in an electrochemical system integrated with H₂ generation and urea-rich wastewater purification.

ZIF-67-Derived NiCo-Layered Double Hydroxide@Carbon Nanotube Architectures with Hollow Nanocage Structures as Enhanced Electrocatalysts for Ethanol Oxidation Reaction

The rational design of efficient Earth-abundant electrocatalysts for the ethanol oxidation reaction (EOR) is the key to developing direct ethanol fuel cells (DEFCs). Among these, the smart structure is highly demanded for highly efficient and stable non-precious electrocatalysts based on transition metals (such as Ni, Co, and Fe). In this work, high-performance NiCo-layered double hydroxide@carbon nanotube (NiCo-LDH@CNT) architectures with hollow nanocage structures as electrocatalysts for EOR were prepared via sacrificial ZIF-67 templates on CNTs. Comprehensive structural characterizations revealed that the as-synthesized NiCo-LDH@CNTs architecture displayed 3D hollow nanocages of NiCo-LDH and abundant interfacial structure between NiCo-LDH and CNTs, which could not only completely expose active sites by increasing the surface area but also facilitate the electron transfer during the electrocatalytic process, thus, improving EOR activity. Benefiting from the 3D hollow nanocages and interfacial structure fabricated by the sacrificial ZIF-67-templated method, the NiCo-LDH@CNTs-2.5% architecture exhibited enhanced electrocatalytic activity for ethanol oxidation compared to single-component NiCo-LDH, where the peak current density was 11.5 mA·cm^-2, and the j_f/j_b value representing the resistance to catalyst poisoning was 1.72 in an alkaline environment. These results provide a new perspective on the fabrication of non-precious metal electrocatalysts for EOR in DEFCs.

Promoting the Electrocatalytic Ethanol Oxidation Activity of Pt by Alloying with Cu

The development and commercialization of direct ethanol fuel cells requires active and durable electro-catalysts towards the ethanol oxidation reactions (EOR). Rational composition and morphology control of Pt-based alloy nanocrystals can not only enhance their EOR reactivity but also reduce the consumption of precious Pt. Herein, PtCu nanocubes (NCs)/CB enclosed by well-defined (100) facets were prepared by solution synthesis, exhibiting much higher mass activity (4.96 A mgPt−1) than PtCu nanoparticles (NPs)/CB with irregular shapes (3.26 A mgPt−1) and commercial Pt/C (1.67 A mgPt−1). CO stripping and in situ Fourier transform infrared spectroscopy (FTIR) experiments indicate that the alloying of Cu enhanced the adsorption of ethanol, accelerated the subsequent oxidation of intermediate species, and increased the resistance to CO poisoning of PtCu NCs/CB, as compared with commercial Pt/C. Therefore, alloying Pt with earth-abundant Cu under rational composition and surface control can optimize its surface and electronic structures and represents a promising strategy to promote the performance of electro-catalysts while reduce the use of precious metals.

Pd-Sb Rhombohedra with an Unconventional Rhombohedral Phase as a Trifunctional Electrocatalyst

Crystal phase engineering is an important strategy for designing noble-metal-based catalysts with optimized activity and stability. From the thermodynamic point of view, it remains a great challenge to synthesize unconventional phases of noble metals. Here, a new class of Pd-based nanostructure with unconventional rhombohedral Pd₂₀ Sb₇ phase is successfully synthesized. Benefiting from the high proportion of the unique exposed Pd₂₀ Sb₇ (003) surface, Pd₂₀ Sb₇ rhombohedra display much enhanced ethanol oxidation reaction (EOR) and oxygen reduction reaction performance compared with commercial Pd/C. Moreover, Pd₂₀ Sb₇ rhombohedra are also demonstrated as an effective air cathode in non-aqueous Li-air batteries with an overpotential of only 0.24 V. Density functional theory calculations reveal that the unique exposed facets of Pd₂₀ Sb₇ rhombohedra can not only reduce the excessive adsorption of CH₃ CO* to CH₃ COOH on Pd for promoting EOR process, but also weaken CO binding and CO poisoning. This work provides a new class of unconventional intermetallic nanomaterials with enhanced electrocatalytic activity.

Combining surface chemical functionalization with introducing reactive oxygen species boosts ethanol electrooxidation

The introduction of functional groups or oxygen vacancies into Pd-based electrocatalysts is a powerful strategy for enhancing the electrocatalytic performances for many electrocatalytic reactions. Herein, an amorphous ceria-modified Pd nanocomposite anchored on D-4-amino-phenylalanine (DAP)-functionalized graphene nanosheets (Pd-CeO_2-x/FGS) was prepared by a facile and effective one-pot synthetic strategy and further used as an electrocatalyst for the ethanol oxidation reaction (EOR) in alkaline electrolytes. The obtained Pd-CeO_2-x/FGS exhibits relatively high electrocatalytic activity, fast kinetics and excellent antipoisoning ability as well as robust durability for EOR, outperforming the comparable electrocatalysts as well as commercial Pd/C. The experimental results show that the enhanced EOR properties of Pd-CeO_2-x/FGS can be attributed to the DAP-functionalization and CeO_2-x-modification. Adequate functional groups (amino and carboxyl groups) and abundant oxygen vacancies were introduced in Pd-CeO_2-x/FGS by DAP-functionalization and CeO_2-x-modification. The functional groups facilitate the anchoring of small nanoparticles onto the substrate as well as modulate the electron density of Pd. The oxygen vacancies boost the adsorption ability of the reactive oxygen species (OH_ads) and accelerate the kinetics of the potential-limiting step for EOR. This study proposes a new strategy for the rational design of highly efficient catalysts for the electro-oxidation reaction.

Highly Selective Wearable Alcohol Homologue Sensors Derived from Pt-Coated Truncated Octahedron Au

Unhealthy alcohol inhalation is among the top 10 causes of preventable death. However, the present alcohol sensors show poor selectivity among alcohol homologues. Herein, Pt-coated truncated octahedron Au (Pt_m@Au_to) as the electrocatalyst for a highly selective electrochemical sensor toward alcohol homologues has been designed. The alcohol sensor is realized by distinguishing the electro-oxidation behavior of methanol (MeOH), ethanol (EtOH), or isopropanol (2-propanol). Intermediates from alcohols are further oxidized to CO₂ by Pt_m@Au_to, resulting in different oxidation peaks in cyclic voltammograms and successful distinction of alcohols. Pt_m@Au_to is then modified on wearable glove-based sensors for monitoring actual alcohol samples (MeOH fuel, vodka, and 2-propanol hand sanitizer), with good mechanical performance and repeatability. The exploration of the Pt_m@Au_to-based wearable alcohol sensor is expected to be suitable for environmental measurement with high selectivity for alcohol homologues or volatile organic compounds.

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.

Facile synthesis of PdSn alloy octopods through the Stranski–Krastanov growth mechanism as electrocatalysts towards the ethanol oxidation reaction

Pd72Sn28 octopods synthesized through the Stranski–Krastanov growth mode exhibited remarkably enhanced catalytic performance for the EOR relative to commercial Pd/C.

Strain effect in Pd@PdAg twinned nanocrystals towards ethanol oxidation electrocatalysis

The strain effect is a critical knob to tune the catalytic performance and has received unprecedented research interest recently. However, it is difficult to distinguish the strain effect from the synergistic effect, especially in alloyed catalysts. Here we have synthesized Pd@PdAg icosahedra and {111} truncated bi-pyramids with only different surface strains between them as electrocatalysts for the ethanol oxidation reaction (EOR). Due to the same exposed facets and compositions of the two electrocatalysts, their EOR performances are mainly determined by the surface strains of PdAg alloys. These two electrocatalysts provide a perfect model to investigate the role of the strain effect in tuning the EOR performance. It is indicated that Pd@PdAg {111} truncated bi-pyramids with a surface strain of 0.3% show better catalytic activity and durability than Pd@PdAg icosahedra with a surface strain of 2.1% including commercial Pd/C. Density functional theory (DFT) calculations reveal that the lowered d-band center of 0.3% strained PdAg alloys relative to 2.1% strained ones reduced the adsorption energy of the acetate-evolution key intermediate *CH₃CO, thereby promoting the enhancement in the catalytic performance of Pd@PdAg nanocrystals for the EOR. Electrochemical analysis further verifies this demonstration on the key role of the strain effect in PdAg alloys for tuning catalytic performance.

Mxene coupled over nitrogen-doped graphene anchoring palladium nanocrystals as an advanced electrocatalyst for the ethanol electrooxidation

Development of good support materials is widely adopted as a valid strategy to fabricate high performance electrocatalysts for the ethanol oxidation reaction (EOR). In this study, the small diameter Ti₃C₂T_x MXene thin nanosheets inserted into three-dimensional nitrogen-doped grapheme (NG) was constructed via a facile hydrothermal method and employed as support materials for anchoring Pd nanocrystals (Pd/Ti₃C₂T_x@NG). The obtained-Pd/Ti₃C₂T_x@NG as EOR electrocatalyst in alkaline media outperforms the commercial Pd/C with better electrocatalytic activity, enhanced long-term stability and high CO tolerance. The Ti₃C₂T_x inserted into NG probably plays a key role for enhancing the properties of the synthesized-catalyst. Inserting Ti₃C₂T_x into NG allows the electrocatalysts to have high porosity, surface hydrophilicity, sufficient number of anchor sites for Pd nanocrystals and modifies its electronic properties, which can promote the electrocatalytic activity and durability. The enhanced EOR performance endows Pd/Ti₃C₂T_x@NG with great application potential in fuel cells as an anode catalyst. Furthermore, the prepared Ti₃C₂T_x@NG is also suitable in various desired applications, especially other oxidation reactions.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Pt3Sn nanoparticles enriched with SnO2/Pt3Sn interfaces for highly efficient alcohol electrooxidation

Pt₃Sn nanoparticles (NPs) enriched with Pt₃Sn/ultra-small SnO₂ interfaces (Pt₃Sn@u-SnO₂/NG) were synthesized through a thermal treatment of Pt₂Sn/NG in a H₂ atmosphere, followed by annealing under H₂ and air conditions. The unique structure of Pt₃Sn NPs enriched with Pt₃Sn/SnO₂ interfaces was observed on the Pt₃Sn@u-SnO₂/NG catalyst based on HRTEM. The optimized Pt₃Sn@u-SnO₂/NG catalyst achieves high catalytic activity with an ethanol oxidation reaction (EOR) activity of 366 mA mg_Pt ^-1 and a methanol oxidation reaction (MOR) activity of 503 mA mg_Pt ^-1 at the potential of 0.7 V, which are eight-fold and five-fold higher than those for the commercial Pt/C catalyst (44 and 99 mA mg_Pt ^-1, respectively). The Pt₃Sn@u-SnO₂/NG catalyst is found to be 3 times more stable and have higher CO tolerance than Pt/C. The outstanding performance of the Pt₃Sn@u-SnO₂/NG catalyst should be ascribed to the synergetic effect induced by the unique structure of Pt₃Sn NPs enriched with Pt₃Sn/SnO₂ interfaces. The synergetic effect between Pt₃Sn NPs and ultra-small SnO₂ increases the performance for alcohol oxidation because the Sn in both Pt₃Sn and SnO₂ favors the removal of CO_ads on the nearby Pt by providing OH_ads species at low potentials. The present work suggests that the Pt₃Sn@u-SnO₂ is indeed a unique kind of efficient electrocatalyst for alcohol electrooxidation.

An evaluation of solvent effects and ethanol oxidation

Understanding liquid-metal interfaces in catalysis is important, as the liquid can speed up surface reactions, increase the selectivity of products, and open up new favorable reaction pathways. In this work we modeled using density functional theory various steps in ethanol oxidation/decomposition over Rh(111). We considered implicit (continuum), explicit, and hybrid (implicit combined with explicit) solvation approaches, as well as two solvents, water and ethanol. We focused on modeling adsorption steps, as well as C-C/C-H bond scission and C-O bond formation reactions. Implicit solvation had very little effect on adsorption and reaction free energies. However, using the explicit and hybrid models, some free energies changed significantly. Furthermore, ethanol solvent had a more considerable impact than water solvent. We observed that preferred reaction pathways for C-C scission changed depending on the solvation model and solvent choice (ethanol or water). We also applied the bond-additivity solvation method to calculate heats of adsorption. Heats of adsorption and reaction using the bond-additivity model followed the same trends as the other solvation models, but were ∼1.1 eV more endothermic. Our work highlights how different solvation approaches can influence analysis of the oxidation/decomposition of organic surface species.

Ordered PdCu-Based Core-Shell Concave Nanocubes Enclosed by High-Index Facets for Ethanol Electrooxidation

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts toward many electrocatalytic reactions. Herein we demonstrate that Au@Pd₁Cu concave nanocubes (CNCs) with an ordered body-centered cubic (bcc) PdCu alloy shell enclosed by many high active high-index facets can be adopted as highly active yet stable electrocatalysts for the ethanol oxidation reaction (EOR). These CNCs are more efficient than other nanocrystals with a disordered face-centered cubic (fcc) PdCu alloy surface and display high mass and specific activities of 10.59 A mg_pd^-1 and 33.24 mA cm^-2, which are 11.7 times and 4.1 times higher than those of commercial Pd black, respectively. Our core-shell CNCs also exhibit robust durability with the weakest decay in activity after 250 potential-scanning cycles, as well as outstanding antipoisoning ability. Alloying with Cu and the ordered bcc phase surface can provide abundant OH_ads species to oxidize carbonaceous poison to avoid catalyst poisoning, and the exposed high-index facets on the surface can act as highly catalytic sites.

Codeposition of Platinum and Gold on Nickel Wire Electrodes via Galvanic Replacement Reactions for Electrocatalytic Oxidation of Alcohols

Codeposition of Pt and Au on Ni wire was performed using a simple treatment of immersing Ni wire in aqueous solutions containing both K2PtCl4 and HAuCl4. For evaluating the electrochemical properties of the thus-prepared electrodes, cyclic voltammograms (CVs) of 1.0 M ethanol in 1.0 M NaOH aqueous solutions were recorded. Compared with Pt- or Au-deposited Ni wire electrodes prepared by treating Ni wire in aqueous solutions of a single component, e.g., 1.0 mM K2PtCl4 or 1.0 mM HAuCl4, a noteworthy increase in the electrocatalytic current was observed for the oxidation of ethanol with a PtAu-codeposited Ni (PtAu/Ni) wire electrode even when it was prepared in an aqueous solution containing both 0.10 mM K2PtCl4 and 0.10 mM HAuCl4. In addition, the shape and the peak potentials of CVs recorded using PtAu/Ni wire electrodes were found to be different from those recorded with the Pt- or Au-deposited Ni wire electrodes. Because the CV responses typical of the PtAu/Ni wire electrodes were observed even when a PtAu/Ni wire electrode was prepared in an aqueous solution containing both 0.010 mM K2PtCl4 and 1.0 mM HAuCl4, it is considered that a small amount of Pt was effectively modified or incorporated and affected the electrochemical properties significantly. The CV results for ethanol oxidation were compared with those for the electrocatalytic oxidations of methanol, 1-propanol, and 2-propanol. Besides, the CV results recorded with the present PtAu/Ni wire electrodes are discussed in comparison with some previous results obtained using other PtAu nanoelectrocatalysts.

Cryoaerogels and Cryohydrogels as Efficient Electrocatalysts

Additive-free cryoaerogel coatings from noble metal nanoparticles are prepared and electrochemically investigated. By using liquid nitrogen or isopentane as cooling medium, two different superstructures are created for each type of noble metal nanoparticle. These materials (made from the same amount of particles) have superior morphological and catalytic properties as compared to simply immobilized, densely packed nanoparticles. The morphology of all materials is investigated with scanning electron microscopy (SEM). Electrochemically active surface areas (ECSAs) are calculated from cyclic voltammetry measurements. The catalytic activity is studied for the ethanol oxidation reaction (EOR). Both are found to be increased for superstructured materials prepared by cryoaerogelation. Furthermore, cryoaerogels with cellular to dendritic structure that arise from freezing with isopentane show the best catalytic performance and highest ECSA. Moreover, as a new class of materials, cryohydrogels are created for the first time by thawing flash-frozen nanoparticle solutions. Structure and morphology of these materials match with the corresponding types of cryoaerogels and are confirmed via SEM. Even the catalytic activity in EOR is in accordance with the results from cryoaerogel coatings. As a proof of concept, this approach offers a novel platform towards the easier and faster production of cryogelated materials for wet-chemical applications.

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 Bio-Templated Metallic Nanomaterial Synthesis and Electrocatalytic Applications

Developing metallic nanocatalysts with high reaction activity, selectivity and practical durability is a promising and active subfield in electrocatalysis. In the classical "bottom-up" approach to synthesize stable nanomaterials by chemical reduction, stabilizing additives such as polymers or organic surfactants must be present to cap the nanoparticle to prevent material bulk aggregation. In recent years, biological systems have emerged as green alternatives to support the uncoated inorganic components. One key advantage of biological templates is their inherent ability to produce nanostructures with controllable composition, facet, size and morphology under ecologically friendly synthetic conditions, which are difficult to achieve with traditional inorganic synthesis. In addition, through genetic engineering or bioconjugation, bio-templates can provide numerous possibilities for surface functionalization to incorporate specific binding sites for the target metals. Therefore, in bio-templated systems, the electrocatalytic performance of the formed nanocatalyst can be tuned by precisely controlling the material surface chemistry. With controlled improvements in size, morphology, facet exposure, surface area and electron conductivity, bio-inspired nanomaterials often exhibit enhanced catalytic activity towards electrode reactions. In this Review, recent research developments are presented in bio-approaches for metallic nanomaterial synthesis and their applications in electrocatalysis for sustainable energy storage and conversion systems.

Recent Progress of Ultrathin 2D Pd-Based Nanomaterials for Fuel Cell Electrocatalysis

Pd- and Pd-based catalysts have emerged as potential alternatives to Pt- and Pt-based catalysts for numerous electrocatalytic reactions, particularly fuel cell-related reactions, including the anodic fuel oxidation reaction (FOR) and cathodic oxygen reduction reaction (ORR). The creation of Pd- and Pd-based architectures with large surface areas, numerous low-coordinated atoms, and high density of defects and edges is the most promising strategy for improving the electrocatalytic performance of fuel cells. Recently, 2D Pd-based nanomaterials with single or few atom thickness have attracted increasing interest as potential candidates for both the ORR and FOR, owing to their remarkable advantages, including high intrinsic activity, high electron mobility, and straightforward surface functionalization. In this review, the recent advances in 2D Pd-based nanomaterials for the FOR and ORR are summarized. A fundamental understanding of the FOR and ORR is elaborated. Subsequently, the advantages and latest advances in 2D Pd-based nanomaterials for the FOR and ORR are scientifically and systematically summarized. A systematic discussion of the synthesis methods is also included which should guide researchers toward more efficient 2D Pd-based electrocatalysts. Lastly, the future outlook and trends in the development of 2D Pd-based nanomaterials toward fuel cell development are also presented.

Hydrogen and Potassium Acetate Co-Production from Electrochemical Reforming of Ethanol at Ultrathin Cobalt Sulfide Nanosheets on Nickel Foam

The sluggish reaction kinetics of the anodic oxygen evolution reaction increases the energy consumption of the overall water electrolysis for high-purity hydrogen generation. In this work, ultrathin cobalt sulfide nanosheets (Co₃S₄-NSs) on nickel foam (Ni-F) nanohybrids (termed as Co₃S₄-NSs/Ni-F) are synthesized using cyanogel hydrolysis and a sulfurization two-step approach. Physical characterizations reveal that Co₃S₄-NSs with a 1.7 nm thickness have abundant holes, implying the big surface area, abundant active edge atoms, and sufficient active sites. Electrochemical measurements show that as-synthesized Co₃S₄-NSs/Ni-F have excellent electrocatalytic activity and selectivity for ethanol oxidation reaction and hydrogen evolution reaction. Due to their bifunctional property of Co₃S₄-NSs/Ni-F nanohybrids, a symmetric Co₃S₄-NSs/Ni-F∥Co₃S₄-NSs/Ni-F ethanol electrolyzer can be effectively constructed, which only requires a 1.48 V electrolysis voltage to reach a current density of 10 mA cm^-2 for high-purity hydrogen generation at the cathode as well as value-added potassium acetate generation at the anode, much lower than the electrolysis voltage of traditional electrochemical water splitting (1.64 V).

Enriching the branching of Au@PdAu core–shell nanocrystals using a syringe pump: kinetics control meets lattice mismatch

Gold@palladium–gold nanocrystals with a tunable branched shape are prepared via seeded growth, where the use of a syringe pump allows the manipulation over reaction kinetics as coupled by surface diffusion and strain caused by lattice mismatch.

Toward Overcoming the Challenges in the Comparison of Different Pd Nanocatalysts: Case Study of the Ethanol Oxidation Reaction

Precious metal nanoparticles, in particular palladium nanomaterials, show excellent catalytic properties and are key in the development of energy systems. For instance, ethanol fuel cells are promising devices for sustainable energy conversion, where Pd-based catalysts are key catalysts for the related ethanol oxidation reaction (EOR). Pd is a limited resource; thus, a remaining challenge is the development of efficient and stable Pd-based catalysts. This calls for a deeper understanding of the Pd properties at the nanoscale. This knowledge can be gained in comparative studies of different Pd nanomaterials. However, such studies remain challenging to perform and interpret due to the lack of cross-studies using the same Pd nanomaterials as a reference. Here, as-prepared sub 3 nm diameter surfactant-free Pd nanoparticles supported on carbon are obtained by a simple approach. The as-prepared catalysts with Pd loading 10 and 30 wt % show higher activity and stability compared to commercially available counterparts for the EOR. Upon electrochemical testing, a significant size increase and loss of electrochemical active surface are observed for the as-prepared catalysts, whereas the commercial samples show an increase in the electrochemically active surface area and moderate size increase. This study shines light on the challenging comparison of different catalysts across the literature. Further advancement in Pd (electro)catalyst design will gain from including self-prepared catalysts. The simple synthesis detailed easily leads to suitable nanoparticles to be used as a reference for more systematic comparative studies of Pd catalysts across the literature.

Au Nanoparticles Modified with Pt, Ru and SnO2 as Electrocatalysts for Ethanol Oxidation Reaction in Acids

The anodic reaction in direct ethanol fuel cells (DEFCs), ethanol oxidation reaction (EOR) faces challenges, such as incomplete electrooxidation of ethanol and high cost of the most efficient electrocatalyst, Pt in acidic media at low temperature. In this study, core-shell electrocatalysts with an Au core and Pt-based shell (Au@Pt) are developed. The Au core size and Pt shell thickness play an important role in the EOR activity. The Au size of 2.8 nm and one layer of Pt provide the most optimized performance, having 6 times higher peak current density in contrast to commercial Pt/C. SnO₂ as a support also enhances the EOR activity of Au@Pt by 1.73 times. Further modifying the Pt shell with Ru atoms achieve the highest EOR current density that is 15 and 2.5 times of Pt/C and Au@Pt. Our results suggest the importance of surface modification in rational design of advanced electrocatalysts.