Graphitized carbon nanocages/palladium nanoparticles: Sustainable preparation and electrocatalytic performances towards ethanol oxidation reaction

Graphitized carbon (GC) nanocages have been successfully prepared via a sustainable carbon powder buried-type Ni catalysis-growth technology from Tween-80 molecule precursor. The GC nanocages are used as support for the further construction of GC/Pd electrocatalyst towards ethanol oxidation reaction. The material structures and surface morphologies are studied by XRD, SEM and TEM techniques. The electrochemical properties are investigated by CV, LSV, EIS and CP techniques. The results showed that GC nanocages have good graphited structure and plentiful opening gaps, and the Pd nanoparticles were evenly distributed on the inner and outer surfaces of GC nanocages. The GC/Pd electrocatalyst exhibits excellent electrocatalytic performance towards ethanol oxidation. The positive scanning peak current density of GC/Pd electrode is up to 1612 A/g Pd in 1.0 mol/L NaOH +1.0 mol/L ethanol electrolyte, which is much higher than those (500–1100 A/g Pd) of traditional Pd electrodes supported with carbon nanotubes or graphene nanosheets.     

Pd nanoparticles on self-doping-defects mesoporous carbon supports for highly active ethanol oxidation and ethylene glycol oxidation

The high activity electrocatalysts with low cost are crucial for large-scale direct alcohol fuel cells (DAFCs) applications. In this study, the “self-doping-defects” mesoporous carbon (SDMC) as support of uniformly-dispersed Pd nanoparticles (Pd/SDMC) was prepared for high active electrooxidation by a simple route without additional surfactant and acid treatment. According to the mutually corroborated experimental and theoretical calculation results, our route can significantly increase the carbon defect, which is conducive to the anchoring and uniform distribution of Pd nanoparticles. Meanwhile, the uniquely and hierarchically mesoporous nanostructure of SDMC provides abundant pathways for mass transport in the electrooxidation reaction. Benefitting from the above advantages, Pd/SDMC exhibits superior activity than commercial Pd/C and previously reported carbon-based electrocatalysts. The mass activities and specific activities of Pd/SDMC toward ethanol oxidation reaction (EOR) are 3404.3 mA mg⁻¹, 4.48 mA cm⁻², respectively. The mass activities and specific activities of Pd/SDMC for ethylene glycol oxidation reaction (EGOR) are 4002 mA mg⁻¹, 5.26 mA cm⁻², respectively. We believe that the facile strategy to synthesis mesoporous carbon with “self-doping” defects would promote large-scale DAFCs applications in the future.     

MoS2 nanoflower supported Pt nanoparticle as an efficient electrocatalyst for ethanol oxidation reaction

Developing highly active and stable ethanol oxidation electrocatalysts is crucial for direct ethanol fuel cells. Herein, platinum/molybdenum disulfide nanoflower (Pt/MoS₂) nanocomposite is synthesized through a facile method and is first applied as catalyst for ethanol oxidation reaction. In situ electrochemical nuclear magnetic resonance is carried out to investigate the electrocatalytic activity of Pt/MoS₂ and the detailed mechanism of ethanol oxidation reaction. Experimental results indicate that in situ electrochemical nuclear magnetic resonance possesses great advantages for real-time investigation of ethanol oxidation reaction, and Pt/MoS₂ is found to exhibit better electrocatalytic performances in terms of higher current density, better stability, and stronger anti-poisoning activity compared to commercial Pt/C and pure Pt catalysts in acid electrolyte, suggesting its potential for application in direct ethanol fuel cells. Density functional theory calculations indicate that MoS₂-supported Pt atom has a smaller energy barrier for the dissociation of ethanol compared to those of Pt and C-supported Pt atom, leading to the enhancement of catalytic activity. This work reveals the importance of the supporting materials for high performance direct ethanol fuel cells catalysts.     

Design the PdCu/Ni2P electrocatalyst with high efficiency for ethanol oxidation reaction in alkaline media

To facilitate the electrocatalytic behavior of Direct Ethanol Fuel Cells (DEFCs), a sequence of bimetallic Pd_xCu_y/Ni₂P-C catalysts are synthesized via the microwave-assisted ethylene glycol reduction method. The results indicate that our designed Pd₂Cu/Ni₂P-C(1:1) catalyst owns high activity (3974.08 mA mg^?1_Pd), 8.3 times higher than the commercial Pd/C. The durability and the CO tolerance of the corresponding catalysts are also investigated by chronoamperometry (CA) and CO stripping measurements, implying Pd₂Cu/Ni₂P-C(1:1) shows good durability and the anti-CO poisoning ability for EOR in alkaline media. The electrochemical impedance spectra (EIS) analysis reveals lower charge transfer resistance for Pd₂Cu/Ni₂P-C(1:1). Combined with the results of XRD, HRTEM, XPS and electrochemical measurements, we found that the good electrocatalytic activity, CO tolerance and long-term durability of Pd₂Cu/Ni₂P-C(1:1) may be provided by the electronic and strain effect among Pd, Cu and Ni₂P, which will bring the downshift in the d-band center of catalysts and the weakened adsorption of intermediates.     

Rational design of PdBi nanochains with grain boundaries for enhanced ethanol oxidation reaction

Over the years, direct ethanol fuel cells have aroused wide concern in sustainable development. At the same time, researchers are committed to developing low-cost and high-efficiency fuel cells, especially catalysts as the core component. In this work, PdBi nanochains (NCs) were synthesized by a brief one-step method and applied as catalysts. Among these PdBi NCs catalysts, the Pd₇₉Bi₂₁ NCs displayed the topmost mass activity of 1.74 A mg_Pd^?1 for ethanol oxidation reaction, which was three times that of commercial Pd/C. In addition, it performed well in terms of temporal stability. According to a series of characterization results, its excellent performance was attributed to several merits: (i) the electronic structure of Pd was modified after doping Bi, which could weaken the interaction between Pd and CO or other intermediates; (ii) defects (the grain boundaries, for instance) would provide abundant active sites in the catalytic reactions; (iii) the nanochain-based structure was conducive to the complete exposure of active reaction sites and the improvement of stability.     

Electrodeposition of nickel nanoparticles on functional MWCNT surfaces for ethanol oxidation

Nickel (Ni) always accumulates on multi-walled carbon nanotubes (MWCNT) by direct electrodeposition. In this paper, nickel nanoparticles were electro crystallized on 4-nitroaniline (NA) radical monolayer-grafted on MWCNT through molecular level design. The structure and nature of the Ni/NA/MWCNT were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the results show that Ni nanoparticles were homogeneously electrodeposited on the surfaces of MWCNT. This complex catalyst showed excellent electro-catalytic activity for oxidation of ethanol in alkaline solution.     

Composites of Ni-MOF and polyaniline hydrogel for carbon monoxide resistant excellent catalysts of ethanol oxidation reaction

EOR is a semi-reaction of direct ethanol fuel cells (DEFCs), and determines the performance of the DEFCs. Therefore, it is very important for EOR to rationally design an electrocatalyst with excellent activity, stability and CO-resistance. Based on this, we report the synthesis of MOF based composite catalysts by a facile method, which is formed by combining polyaniline hydrogel (PANH) with MOF 1 and carbon cloth (CC). At the same time, the structures of the composites were characterized by XRD, SEM and XPS. Under the optimum conditions, the j value for EOR is 107 mA cm^?2 under alkaline conditions at 0.6 V, which indicates that composite 2 has excellent catalytic activity for EOR, and is superior to that of the previously reported nickel-based catalysts for EOR. The Tafel slope and the exchange current density of composite 2 are 88.9 mV dec^?1 and 1.95 × 10^?5 A cm^?2 respectively. In addition, the j value of composite 2 was 65% of the original value after 1000 CV cycles. However, when the electrolyte was changed into the original one (1 M KOH + 1 M EtOH), the j value returned to 74% of the original value. Based on the excellent electrocatalytic performance, good stability and anti-CO poisoning, composite 2 is expected to be an economic, efficient and CO poisoning resistant electrocatalyst for EOR.     

Pd/Hemin-rGO as a bifunctional electrocatalyst for enhanced ethanol oxidation reaction in alkaline media and hydrogen evolution reaction in acidic media

H₂ generation needs a cost-effective, robust, stable, long-durable, and super-active electrocatalyst. This study reveals a rapid and facile method for fabricating Pd NPs on Hemin-rGO as novel support. The obtained electrocatalyst was characterized by UV–Vis, XPS, FESEM, EDS, HRTEM, and AFM. The electrochemical measurements reveal the superb effect of Hemin-rGO for enhancing the catalytic activity of Pd as bifunctional electrocatalysts for hybrid water electrolysis (hydrogen evolution reaction (HER) and ethanol electrooxidation reaction (EOR)). Pd/Hemin-rGO displays a low peak potential (−210 V) with remarkable current density (1.95 A mg⁻¹ Pd) in 0.1 M EtOH and 0.1 M NaOH. The ratio of j_f/j_b of Pd/Hemin-rGO compared with Pd electrocatalyst reveals this novel support's ani-poisoning effect. Besides, it shows the Tafel slope of 26 mV dec⁻¹ and overpotentials of 47 and 131 mV were obtained at 10 and 100 mA cm⁻² in acidic media toward HER. Exploring and designing new electrocatalysts may be enhanced by this research, which can use Hemin as a novel support for noble metals such as Pt, Pd, Rh, Au, and Ru for diverse energy-related applications.     

Carbon nanodots prepared from NaOH-boiled graphene and its usage as a support of PdO for ethanol oxidation reaction

For the first time, carbon nanodots were prepared from NaOH-boiled graphene. And, a novel catalyst that contained PdO and carbon nanodots (denoted as PdO/CND) was fabricated in this work. In this work, 0.5 M and 1.5 M NaOH solutions were respectively employed with an intention to study the influence of NaOH concentration on the electrocatalytic activity of the obtained catalysts for ethanol oxidation reaction (EOR). The obtained samples were thoroughly characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared spectrometry (FTIR). The results indicated that the intensities of the diffraction peaks for graphene were significantly promoted with increasing the NaOH concentration and carbon nanodots with an average particle size less than 4 nm were fabricated by this developed boiling–grinding–ultrasonication (BGU) method. The electrocatalytic performances of the obtained PdO/CND catalysts for EOR were investigated using cyclic voltammetry (CV) and chronoamperometry (CA). And the consequences strongly demonstrated that PdO/CND prepared from 0.5 M NaOH-boiled graphene showed the best electrocatalytic activity towards EOR among all the prepared catalysts. Developing a very facile method for producing carbon nanodots as well as a novel composite catalyst that contained PdO and carbon nanodots for EOR was the main contribution of this work.     

One-pot synthesis of PdZnO/C by microwave sintering method as an efficient electro catalyst for ethanol oxidation reaction

The PdZnO/C catalytic material for ethanol oxidation reaction is prepared by microwave heating-glycol reduction method. PdZnO is well polymerized and dispersed on XC72. The results demonstrate that PdZnO/C has better electro catalytic activity and stability for ethanol oxidation reaction than Pd/C at room temperature. ZnO/C shows no catalysis for ethanol oxidation. The oxidation peak potential of PdZnO/C electrode is shifted negatively to 0.21 V. The current density of PdZnO/C electrode is 145 mA cm⁻², while that of the Pd/C electrode is 60 mA cm⁻². Moreover, single cell discharge test shows that discharge voltage of the PdZnO/C electrode reaches to 0.41 V at 30 mA cm⁻². In summary, ZnO as a co-catalyst significantly improves the activity of PdZnO/C catalyst for ethanol oxidation reaction.     

Insights on the ethanol oxidation reaction at electrodeposited PdNi catalysts under conditions of increased mass transport

The development of high-performance electrocatalysts for alcohol oxidation is still a major challenge to use these reactions for sustainable energy applications such as hydrogen production. In addition, understanding the reactivity under different hydrodynamic conditions is essential since the fuel is continuously fed to the anode in practical applications. In this work, the synthesis, characterization and electroactivity of bimetallic PdNi nanocoatings generated by electrodeposition toward the ethanol oxidation reaction (EOR) is described. A catalyst formed by Pd_0.91Ni_0.09 nanoflowers showed the highest EOR activity and enhanced performance under moderate mass transport rate. Both OH^? concentration and hydrodynamics affected the EOR activity and the product selectivity. Acetic acid was the main EOR product, but acetaldehyde formation increased when OH^? was limiting or under faster mass transport rates. This study provides novel knowledge to understand the EOR on PdNi catalysts and exposes the importance of evaluating hydrodynamic conditions when developing new electrocatalysts.     

Enhanced electrocatalytic activity and stability of Pd nanoparticles supported on TiO2-modified nitrogen-doped carbon for ethanol oxidation in alkaline media

TiO₂-modified nitrogen-doped carbon (TiO₂-NC), prepared by a polymerization-pyrolysis process, is used to support the Pd catalyst for ethanol oxidation reaction (EOR) in alkaline media. X-ray photoelectron spectroscopy characterization indicates that the incorporation of TiO₂ and nitrogen into the carbon matrix could improve the percentage of Pd⁰ in Pd/TiO₂-NC catalyst. Electrochemical characterization shows that the Pd/TiO₂-NC catalyst presents higher electrocatalytic activity and stability for EOR than the nitrogen-doped carbon-supported Pd (Pd/NC) catalyst and the carbon black-supported Pd (Pd/CB) catalyst, which can be mainly attributed to the high percentage of Pd⁰ in Pd/TiO₂-NC catalyst (65%) than those in Pd/NC (48%) and Pd/CB (31%) catalysts. The results indicate that the Pd/TiO₂-NC catalyst holds great potential as high-performance anode catalyst for direct ethanol fuel cells.     

Using PdO and PbO as the starting materials to prepare a multi-walled carbon nanotubes supported composite catalyst (PdxPby/MWCNTs) for ethanol oxidation reaction (EOR)

For the first time, a novel composite catalyst, namely, a multi-walled carbon nanotubes (MWCNTs) supported palladium and lead catalyst (denoted as Pd_xPb_y/MWCNTs), was prepared through a hydrothermal method using PdO, PbO and MWCNTs as the starting materials. The electrocatalytic activities of the resultant catalysts towards EOR in 1M KOH were examined mainly by using CV, CA and EIS. The electrochemical measurement results indicated that the peak current of EOR in the forward potential scan on the catalyst of Pd₁Pb₁/MWCNTs was almost 9 times larger, plus about 100 mV decrease in the onset potential value of EOR, than that on the Pb-free catalyst. A very simple, cost-effective and scalable way to synthesize Pd and Pb composite electrocatalyst for EOR was presented in this work, which was very meaningful to the further commercialization of EOR.     

Electrocatalytic activity of core-shell Au@Pt nanoparticles for the hydrogen oxidation reaction

The hydrogen oxidation reaction (hor) was studied for the first time on core-shell Au@Pt nanoparticles. They were dispersed on a rotating gold disc, with four different values of the active area factor (0.03 < f_aa < 2). The experimental current-overpotential dependences on steady state for the hor were obtained at a rotation rate of 2500 rpm. The elementary kinetic parameters were evaluated and compared with previous results obtained for platinum nanoparticles. It can be concluded that the substitution of the core of a Pt nanoparticle by Au would lead to a slight decrease of the reaction rate of the Tafel step (chemical), but it would not affect the charge transfer steps. Thus, the electrocatalytic activity of the Au@Pt nanoparticles is slightly lower than that of Pt nanoparticles at low overpotentials, but they are equal for η > 0.20 V.     

1D-2D integrated hybrid carbon nanostructure supported bimetallic alloy catalyst for ethanol oxidation and oxygen reduction reactions

Herein, 1-D carbon nanotubes and 2-D graphene hybrid carbon hetero-structure is employed as the catalyst support material for low temperature fuel cell. Partial unraveling of carbon nanotubes results in 1D-2D hybrid hetero-structure with enhanced surface area, while the intact inner tubes result in good electrical conductivity. Platinum-tin alloy decorated on partially exfoliated carbon nanotubes (Pt–Sn/PCNT) were prepared by ethylene glycol reduction method and investigated its electrocatalytic activity towards ethanol oxidation reaction (EOR) for direct ethanol fuel cell (DEFC) and oxygen reduction reaction (ORR) for hydrogen fuelled polymer electrolyte membrane fuel cell (PEMFC). Along with the intrinsic properties of carbon nanotubes, PCNT provides more anchoring sites, thereby facilitates complete utilization of catalysts. The electrochemical EOR studies reveal that Pt–Sn/PCNT has better tolerance to the accumulation of intermediate species than Pt–Sn/CNT. Besides, as-synthesized electrocatalysts exhibit good ORR activity with four-electron pathway. The enhanced EOR and ORR activity of as prepared electrocatalysts is attributed to the high dispersion of catalyst nanoparticles on PCNT along with the inhibition of production of intermediate species on the Pt surface by alloying. Further, the practical suitability of PCNT supported Pt–Sn nanocatalysts as EOR and ORR electrocatalysts has been examined by performing the full fuel cell measurements.     

Controllable synthesis of PtPd nanocubes on graphene as advanced catalysts for ethanol oxidation

PtPd nanocubes (NCs) were uniformly deposited on the reduced graphene oxides (RGOs) via a one-pot solvothermal reduction. These PtPd NCs were enclosed with (100) facet. Their size can be tuned from 11 to 27 nm by controlling their composition. Under the optimum atomic ratio of Pt/Pd (1:5), the as-prepared RGO-supported PtPd NCs show a superior catalytic efficiency of ethanol oxidation reaction (EOR) with a specific activity of 2.3 mA cm^?2 and a mass activity of 1.08 A mg^?1 Pt, far above those for the RGO-supported Pt nanoparticles (0.3 mA cm^?2 for specific activity and 0.018 A mg^?1 Pt for mass activity). Besides, these EOR catalysts exhibit a high CO-tolerance without significant current decay during steady-state polarization at 0.6 V over 4000 s. Their durability is also remarkable with only 8.9% loss of their electrochemical surface area (ECSA) after 10 000 cycles of voltammetric test.     

Activation effect of silver nanoparticles on the photoelectrochemical performance of mesoporous TiO2 nanospheres photoanodes for water oxidation reaction

This work reports the photodeposition of Ag nanoparticles onto mesoporous TiO₂ (m-TiO₂) pre-formed by the evaporation-induced self-assembly method. Photoanodes of Ag/m-TiO₂ assembled by electrophoretic disclose a superior photoelectrochemical (PEC) performance for water oxidation reaction related to m-TiO₂. The photoanodes physicochemical investigations witness the even arrangement of m-TiO₂ nanospheres particles over the substrates. The PEC study displays a steady photocurrent density of 1 mAcm^?2 at ?1.0 V vs SCE was attained for Ag/m-TiO₂ photoanodes in visible light illumination and it is nearly twofold enhancements in comparison with m-TiO₂ photoanodes. The observed superior PEC nature was attributed to the reduced band-gap energy and charge recombination that caused from the incorporation of plasmonic photodeposited Ag nanoparticles on m-TiO₂ nanospheres photoanodes.     

Unexpected facilitation of the pyrolysis products of potassium ferrocyanide to the electrocatalytic activity of a PdO based palladium iron composite catalyst towards ethanol oxidation reaction (EOR)

It was found, for the first time, that the pyrolysis products of potassium ferrocyanide (K₄[Fe(CN)₆]) could significantly promote the electrocatalytic activity of the PdO based palladium iron composite catalyst towards ethanol oxidation reaction (EOR). In this work, huge carbon spheres (abbreviated as HCSs) were prepared firstly via a pyrolysis method using glucose and 1-butyl-3-methylimidazolium tetrafluoroborate as the starting materials. Secondly, PdO based palladium iron composites supported on HCSs (noted as PdO–Pd–Fe/HCSs) were successfully fabricated through a pyrolysis procedure employing PdO·H₂O, HCSs and K₄[Fe(CN)₆] as the initial materials. When preparing PdO–Pd–Fe/HCSs, four different amounts of K₄[Fe(CN)₆] were respectively added in the preparation system producing four kinds of samples. The sample prepared in the absence of K₄[Fe(CN)₆] was nominated as sample b-0. And the samples prepared in the presence of 5, 10 and 20 mg K₄[Fe(CN)₆] were, respectively, labeled as sample b-5, b-10 and b-20. It was indicated by the XRD and XPS patterns that the metallic Pd particles were the main crystalline materials of above four samples. SEM images of all synthesized samples substantially demonstrated that the added amount of K₄[Fe(CN)₆] was a pivotal factor which could significantly affect the morphologies of the prepared samples. For sample b-0, besides some nanoparticles with a size close to 30 nm, a larger number of pores were created on the surface of the HCSs producing a honeycomb-shaped surface. Interestingly, aniseed shaped particles, cauliflower-like particles and irregular particles with a diameter more than 150 nm were, respectively, anchored on the HCSs surface of sample b-5, b-10 and b-20. Most of all, as indicated by CV and CA measurements, all the samples prepared in the presence of K₄[Fe(CN)₆] delivered much better electrocatalytic activities towards EOR when compared to the sample prepared with no addition of K₄[Fe(CN)₆]. For example, in the CV curves, the peak current density of the peak appearing in the positive potential scanning (peak f) for EOR on sample b-10 was nearly 6.4 times greater than that on sample b-0 (16.6 mA cm^?2 vs. 2.6 mA cm^?2). The significantly decreased charge transfer resistance and the remarkably enlarged electrochemical surface area were analyzed to be the main reasons for sample b-10 to exhibit the best electrocatalytic performance among all prepared samples. In general, a novel electrocatalyst consisting of PdO, Pd and the pyrolysis products of K₄[Fe(CN)₆] for EOR was developed in this work, which, due to its very lower preparation cost and its satisfied electrocatalytic activity towards EOR, was very helpful to the development of Pd-based EOR electrocatalyst.     

PtSnCe/C electrocatalysts for ethanol oxidation: DEFC and FTIR “in-situ” studies

The ethanol oxidation reaction (EOR) was investigated using PtSnCe/C electrocatalysts in different mass ratios (72:23:5, 68:22:10 and 64:21:15) that were prepared by the polymeric precursor method. Transmission electron microscopy (TEM) showed that the particles ranged in size from approximately 2 to 5 nm. Changes in the net parameters observed for Pt suggest the incorporation of Sn and Ce into the Pt crystalline network with the formation of an alloy between Pt, Sn and/or Ce. Among the PtSnCe catalysts investigated, the 68:22:10 composition showed the highest activity toward ethanol oxidation, and the current-time curves obtained in the presence of ethanol in acidic media showed a current density 50% higher than that observed for commercial PtSn/C (E-Tek). During the experiments performed on single direct ethanol fuel cells, the power density for the PtSnCe/C 68:22:10 anode was nearly 40% higher than the one obtained using the commercial catalyst. Data from Fourier transform infrared (FTIR) spectroscopy showed that the observed behavior for ethanol oxidation may be explained in terms of a double mechanism. The presence of Sn and Ce seems to favor CO oxidation, since they produce an oxygen-containing species to oxidize acetaldehyde to acetic acid.     

Highly dispersed and COad-tolerant Ptshell-Pdcore catalyst for ethanol oxidation reaction: Catalytic activity and long-term durability

Highly dispersed Pt_shell-Pd_core catalyst is synthesized via an electroless deposition and a galvanic displacement. From electrochemical analysis, the catalyst is confirmed to be active toward an ethanol oxidation reaction for a prolonged time, and is more resistive against CO_ad-poisoning than a conventional Pt/C catalyst. The stable activity of Pt_shell-Pd_core/C is ascribed to the modified electronic property of Pt over-layer, which leads to a weak CO-adsorption strength with a high affinity for OH. The weakened binding property of surface Pt with CO_ad was experimentally confirmed by conducting a CO_ad-stripping and by measuring an electrochemically active surface area of the catalyst over multiple cycles. The CO_ad oxidation ability of as-synthesized catalyst is further proved by a computational method via density functional theory (DFT) calculation. The result presents a potential application of the catalyst for the efficient ethanol oxidation in a direct ethanol fuel cell.