Investigation of ethanol electrooxidation on a Pt–Ru–Ni/C catalyst for a direct ethanol fuel cell

This research is aimed to improve the utilization and activity of anodic alloy catalysts and thus to lower the contents of noble metals and the catalyst loading on anodes for ethanol electrooxidation. The DEFC anodic catalysts, Pt–Ru–Ni/C and Pt–Ru/C, were prepared by a chemical reduction method. Their performances were tested by using a glassy carbon working electrode and cyclic voltammetric curves, chronoamperometric curves and half cell measurement in a solution of 0.5 mol L⁻¹ CH₃CH₂OH and 0.5 mol L⁻¹ H₂SO₄. The composition of the Pt–Ru–Ni and Pt–Ru surface particles were determined by EDAX analysis. The particle size and lattice parameter of the catalysts were determined by means of X-ray diffraction (XRD). XRD analysis showed that both of the catalysts exhibited face centered cubic structures and had smaller lattice parameters than a Pt-alone catalyst. Their particle sizes were small, about 4.5 nm. No significant differences in the ethanol electrooxidation on both electrodes were found using cyclic voltammetry, especially regarding the onset potential for ethanol electrooxidation. The electrochemically active specific areas of the Pt–Ru–Ni/C and Pt–Ru/C catalysts were almost the same. But, the catalytic activity of the Pt–Ru–Ni/C catalyst was higher for ethanol electrooxidation than that of the Pt–Ru/C catalyst. Their tolerance to CO formed as one of the intermediates of ethanol electrooxidation, was better than that of the Pt–Ru/C catalyst.     

Promising anode candidates for direct ethanol fuel cell: Carbon supported PtSn-based trimetallic catalysts prepared by Bönnemann method

To find an efficient anode catalyst for ethanol electrooxidation, several trimetallic PtSnM/C (M = Ni, Co, Rh, Pd) and their corresponding bimetallic PtX/C (X = Sn, Ni, Co, Rh, Pd) catalysts were synthesized by Bönnemann's colloidal precursor method and evaluated by comparing their electrocatalytic activity using conventional electrochemical techniques. For better understanding of the catalyst deactivation during the ethanol electrooxidation, chronoamperometric test was also combined to X-ray photoelectron spectroscopy (XPS) analysis. A significant finding is that trimetallic compositions PtSnCo/C and PtSnNi/C have enhanced activity compared to that of PtSn/C, with lower onset potential for ethanol electrooxidation and notably improved peak current densities. Thus the presence of Ni and Co heteroatom seems to promote C–C bond cleavage and facilitate the removal from the catalyst surface of adsorbed intermediates. These trends are satisfactorily confirmed by testing in a direct ethanol fuel cell (DEFC), since trimetallic PtSnNi/C and PtSnCo/C anode catalysts have significantly higher overall performance and peak power density than Pt/C, PtSn/C or other trimetallic catalyst compositions PtSnRh/C or PtSnPd/C. Furthermore, the presence of Ni or Co helps to improve the weak stability of PtSn/C by providing a stronger Pt–carbon support interaction. XPS results revealed that the surface Pt/Sn atomic ratio of PtSnNi/C catalyst only slightly decreased even after 12 h at 500 mV. On the other hand, a higher concentration of oxide species appeared on the treated PtSn/C surface as a result of a high degradation of carbon support.     

Electrochemical impedance studies on carbon supported PtRuNi and PtRu anode catalysts in acid medium for direct methanol fuel cell

The anodic Pt–Ru–Ni/C and the Pt–Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out by using a glassy carbon working electrode covered with the catalyst powder in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ at 25 °C. EIS information discloses that the methanol electrooxidation on the Pt–Ru–Ni/C catalyst at various potentials shows different impedance behaviors. The mechanism and the rate-determining step of methanol electrooxidation are changed with increasing potential. Its rate-determining steps are the methanol dehydrogenation and the oxidation reaction of adsorbed intermediate CO_ads and OH_ads in low (400–500 mV) and high (600–800 mV) potentials, respectively. The catalytic activity of the Pt–Ru–Ni/C catalyst is higher for methanol electrooxidation than that of the Pt–Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol dehydrogenation is also better than that of the Pt–Ru/C catalyst.     

Ethanol oxidation on Pd/C enhanced by MgO in alkaline medium

The effect of addition MgO to Pd/C catalyst on electrochemical oxidation for ethanol has been studied in alkaline medium. The results show that the reaction activity and the poisoning resistance for ethanol electrooxidation have been significantly improved by addition MgO into Pd/C catalysts. The catalyst with a weight ratio of Pd to MgO of 2:1 gives the best performance. The values of onset potential and peak potential on the Pd–MgO/C electrode are more negative than that on the Pd/C electrode because of synergistic effect between Pd and MgO. By adding MgO to the Pd/C, the value of onset potential negatively shifts more 80 mV and the value of peak current density is 3.4 times higher than that on the Pd/C electrode for ethanol electrooxidation.     

Atomic interface engineering: Strawberry-like RuO2/C hybrids for efficient hydrogen evolution from ammonia borane and water

Efficient hydrogen production plays a key role in establishing hydrogen economy in the current world. In this study, we fabricated ultrafine RuO₂ nanoparticles on carbon black to form a strawberry-like RuO₂/C hybrid, using by a solid-phase grinding and subsequent low-temperature annealing. The synthesized hybrid displays very low reaction activation energy (28.5 KJ mol^?1) for hydrogen evolution from ammonia borane. In case of hydrogen evolution from alkaline water, it also exhibits a remarkably improved electrocatalytic activity than a commercial Pt/C, with an ultra-low overpotential of 8 mV (at 10 mA cm^?2). For the above bifunctional catalyst, the formed C–Ru–C bonds between the ruthenium oxide and carbon result in the ultrahigh activity of the hybrid, as evidenced by DFT results. This work offers a guideline to synthesize efficient metal-based (Ru, Pd, Rh, Ir, Au, etc.) catalysts with smart structures for catalysis.     

Boosting hydrogen evolution activity and durability of Pd–Ni–P nanocatalyst via crystalline degree and surface chemical state modulations

Developing efficient, durable, and economical electro-catalysts for large-scale commercialization of hydrogen evolution (HER) is still challenging. Herein, we report for the first time, to the best of our knowledge, a Pd-based ternary metal phosphide as an active and stable HER catalyst. The face-centered-cubic Pd–Ni–P nanoparticles (NPs) annealed at 400 °C show the best HER activity with a low overpotential of 32 mV to realize a current density of 10 mA cm⁻² and a high mass activity of 1.23 mA μg⁻¹_Pd, superior to Pd NPs, Pd–P NPs, Pd–Ni NPs, and Pd–Ni–P NPs annealed under different temperatures. Moreover, this catalyst is also highly stable during 20 h of continuous electrolysis. Notably, the easily fabricated Pd–Ni–P NPs are among the most active Pd-based HER catalysts. This work indicates that Pd-based metal phosphides could be potentially applied as a type of practical HER catalyst and might inform the fabrication of analogous materials for hydrogen-related applications.     

Pd decorated Co–Ni nanowires as a highly efficient catalyst for direct ethanol fuel cells

The storage and conversion of energy necessitates the use of appropriate electrochemical systems and chemical reaction catalysts. This work presents newly developed catalysts for electrooxidation of ethanol in an alkaline medium. Nanocatalysts composed of Co–Ni nanowires (Co–Ni NWs) decorated with Pd nanoparticles (Pd NPs) were made at varying metal ratios and their chemical composition and structure was investigated in detail. The synthesis involved a wet chemical reduction assisted by a magnetic field, which led to the generation of NWs, followed by the deposition of spherical Pd NPs on their surface. The best catalytic activity was obtained for the catalyst made of Co₃–Ni₇ decorated with Pd NPs, which exhibited EOR of 8003 mA/mg_Pd for only 0.86 wt% of Pd loading. The results can be explained by the synergistic effect between the morphology of the bimetallic support and the favorable interaction of oxophilic Co, Ni with catalytic Pd.     

Pd-Ni electrocatalysts for efficient ethanol oxidation reaction in alkaline electrolyte

Pd_xNi_y/C catalysts with high ethanol oxidation reaction (EOR) activity in alkaline solution have been prepared through a solution phase-based nanocapsule method. XRD and TEM show Pd_xNi_y nanoparticles with a small average diameter (2.4-3.2 nm) and narrow size distribution (1-6 nm) were homogeneously dispersed on carbon black XC-72 support. The EOR onset potential on Pd₄Ni₅/C (−801 mV vs. Hg/HgO) was observed shifted 180 mV more negative than that of Pd/C. Its exchange current density was 33 times higher than that of Pd/C (41.3 × 10⁻⁷ A/cm²vs. 1.24 × 10⁻⁷ A/cm²). After a 10,000-s chronoamperometry test at −0.5 V (vs Hg/HgO), the EOR mass activity of Pd₂Ni₃/C survived at 1.71 mA/mg, while that of Pd/C had dropped to 0, indicating Pd_xNi_y/C catalysts have a better ’detoxification’ ability for EOR than Pd/C. We propose that surface Ni could promote refreshing Pd active sites, thus enhancing the overall ethanol oxidation kinetics. The nanocapsule method is able to not only control over the diameter and size distribution of Pd-Ni particles, but also facilitate the formation of more efficient contacts between Pd and Ni on the catalyst surface, which is the key to improving the EOR activity.     

Pd electrodeposition on a novel substrate of reduced graphene oxide/ poly(melem-formaldehyde) nanocomposite as an active and stable catalyst for ethanol electrooxidation in alkaline media

Palladium nanoparticles (Pd NPs) were successfully electrodeposited on a reduced graphene oxide/poly(melem-formaldehyde) nanocomposite (rGO/PMF) NC as a catalyst for ethanol electrooxidation in alkaline media; melem was used as a nitrogen-rich source in the substrate structure for the first time. The specific surface area and average pore diameter of (rGO/PMF) NC were 481.61 m² gr^?1 and 10.23 nm, respectively. High nitrogen doping and structural defects improved the dispersion and anchoring of Pd NPs on (rGO/PMF) NC. The onset potential (E_onset) of Pd/(rGO/PMF) NC was shifted negatively to 110 mV, in comparison to Pd/rGO. Also, the current density and electrochemical active surface area (EASA) of Pd/(rGO/PMF) NC were enhanced to 44 mA cm^?2 and 67.58 m² gr^?1, respectively, as compared to Pd/rGO. Furthermore, the stability of Pd/(rGO/PMF)NC was indicated against ethanol oxidation intermediates during 7000 s. This work also produced a superior graphene-based material for direct ethanol fuel cell anode catalysts applications.     

Synthesis of PdNi catalysts for the oxidation of ethanol in alkaline direct ethanol fuel cells

Carbon-supported PdNi catalysts for the ethanol oxidation reaction in alkaline direct ethanol fuel cells are successfully synthesized by the simultaneous reduction method using NaBH₄ as reductant. X-ray diffraction characterization confirms the formation of the face-centered cubic crystalline Pd and Ni(OH)₂ on the carbon powder for the PdNi/C catalysts. Transmission electron microscopy images show that the metal particles are well-dispersed on the carbon powder, while energy-dispersive X-ray spectrometer results indicate the uniform distribution of Ni around Pd. X-ray photoelectron spectroscopy analyses reveal the chemical states of Ni, including metallic Ni, NiO, Ni(OH)₂ and NiOOH. Cyclic voltammetry and chronopotentiometry tests demonstrate that the Pd₂Ni₃/C catalyst exhibits higher activity and stability for the ethanol oxidation reaction in an alkaline medium than does the Pd/C catalyst. Fuel cell performance tests show that the application of Pd₂Ni₃/C as the anode catalyst of an alkaline direct ethanol fuel cell with an anion-exchange membrane can yield a maximum power density of 90 mW cm⁻² at 60 °C.     

Ethanol oxidation on PtRuMo/C catalysts: In situ FTIR spectroscopy and DEMS studies

The electrooxidation of ethanol on carbon supported PtRuMo nanoparticles of different Mo compositions has been studied in the temperature range of 30–70 °C. Current–time curves have shown an increase of the current density with the Mo introduction during the ethanol oxidation at 0.5 V in a whole temperature range. The incorporation of different amount of MoO_x (∼Mo⁵⁺) like species over PtRu systems produces ternary catalyst with similar structural characteristics as particle size or crystal phases, but the catalytic behavior depended on both the surface amount of Mo and on the applied potential. In situ spectroelectrochemical studies have been used to identity adsorbed reaction intermediates and products (in situ Fourier transform infrared spectroscopy, FTIR) and volatile reaction products (differential electrochemical mass spectrometry, DEMS). For all catalysts, incomplete ethanol oxidation to C2 products (acetaldehyde and acetic acid) prevails under the conditions selected in this study. The higher CO tolerance of PtRuMo/C catalysts at very low potentials (<0.3 V) results to minimum or no CO poisoning of the Pt and Ru surfaces, in contrast to the PtRu/C catalyst, which are rapidly blocked by CO. Therefore, catalyst with higher amount of Mo allows a fast “replenishment” of the active sites leading to the formation of acetaldehyde and, especially, acetic acid at potentials above 0.3 V.     

Promotional roles of Ru and Sn in mesoporous PtRu and PtRuSn catalysts toward ethanol electrooxidation

The roles of Ru and Sn in mesoporous PtRu and PtRuSn alloys for ethanol electrooxidation reaction were investigated. The catalyst samples were prepared via co-reduction of metal precursors in an aqueous domain of lyotropic liquid crystalline phase of a nonionic surfactant. The crystallite sizes, obtained from x-ray diffractograms of mesoporous PtRu and PtRuSn catalysts, were approximately the same at 3.6 nm. There was a good agreement between the measured lattice parameter and the one calculated from a modification of Vegard's Law suggesting that the ternary PtRuSn alloy had formed. From XPS analysis, the surface species of Ru in both catalysts is in metallic form while Sn in PtRuSn is in SnO phase. The electrochemical measurements in ethanol solution revealed that PtRuSn had exhibited a lower onset potential by about 0.1 V, and also produced a significantly higher oxidation current density than had PtRu. In addition, the chronoamperometry tests demonstrated a lower poisoning rate for ethanol oxidation on the PtRuSn surface at the low potential of 0.3 V vs RHE. However, the adsorbed poisoning species had been effectively oxidized from the surface of PtRu, and consequently shown to be the most poison-tolerant catalyst at a high potential of 0.6 V and a high temperature (60 °C). As a result, Ru and Sn addition exhibited different promotional effects for ethanol oxidation. The addition of Sn promoted dissociative adsorption of ethanol molecules, while the addition of Ru activated the water molecules, which was followed by the oxidation of the strongly adsorbed CO. The added Ru and Sn had enhanced the overall ethanol oxidation on the PtRuSn catalyst.     

Oxidative catalytic steam gasification of sugarcane bagasse for hydrogen rich syngas production

Reactive Flash Volatilization (RFV) is an emerging thermochemical method to produce tar free hydrogen rich syngas from waste biomass at relatively lower temperature (<900 °C) in a single stage catalytic reactor within a millisecond residence time. Here, we show catalytic RFV of bagasse using Ru, Rh, Pd, or Re promoted Ni/Al₂O₃ catalysts under steam rich and oxygen deficient environment. The optimum reaction conditions were found to be 800 °C, steam to carbon ratio = 1.7 and carbon to oxygen ratio = 0.6. Rh–Ni/Al₂O₃ performed the best, resulting in highest hydrogen concentration in the synthesis gas at 54.8%, with a corresponding yield of 106.4 g-H₂/kg bagasse. A carbon conversion efficiency of 99.96% was achieved using Rh–Ni, followed by Ru–Ni, Pd–Ni, Re–Ni and mono metallic Ni catalyst in that order. Alkali and Alkaline Earth Metal species present in the bagasse ash and char, that deposited on the catalyst, was found to enhance its activity and stability. The hydrogen yield from bagasse was higher than previously reported woody biomass and comparable to the microalgae.     

Evaluation of Pt–Ru–Ni and Pt–Sn–Ni catalysts as anodes in direct ethanol fuel cells

In this study, the electrooxidation of ethanol on carbon supported Pt–Ru–Ni and Pt–Sn–Ni catalysts is electrochemically studied through cyclic voltammetry at 50 °C in direct ethanol fuel cells. All electrocatalysts are prepared using the ethylene glycol-reduction process and are chemically characterized by energy-dispersive X-ray analysis (EDX). For fuel cell evaluation, electrodes are prepared by the transfer-decal method. Nickel addition to the anode improves DEFC performance. When Pt₇₅Ru₁₅Ni₁₀/C is used as an anode catalyst, the current density obtained in the fuel cell is greater than that of all other investigated catalysts. Tri-metallic catalytic mixtures have a higher performance relative to bi-metallic catalysts. These results are in agreement with CV results that display greater activity for PtRuNi at higher potentials.     

One-step CO assisted synthesis of hierarchical porous PdRuCu nanosheets as advanced bifunctional catalysts for hydrogen evolution and glycerol oxidation

Pd-based catalysts have received wide attention due to their outstanding anti-CO poisoning property, whereas the structural instability limits their application. The hierarchical porous PdRuCu nanosheets (HP PdRuCu NSs) with large electrochemically active surface area, abundant active sites, and stable structures are synthesized through continuous access to CO bubbles. HP PdRuCu NSs exhibit excellent hydrogen evolution reaction (HER) catalytic activity with an ultralow overpotential of 25 mV at 10 mA cm^?2 and a Tafel slope of 87.5 mV dec^?1 in alkaline·media. Meanwhile, the peak mass activity and specific activity of HP PdRuCu NSs for glycerol oxidation reaction (GOR) are 1083 mA mg^?1_Pd and 38.8 A m^?2, respectively, superior to that of PdRu nanosheets (PdRu NSs), Pd nanosheets (Pd NSs), and commercial Pd black. The introduction of Ru and Cu atoms facilitates the C–C bond cleavage and the complete oxidation of glycerol to CO₂, as well as the accelerated oxidation/removal of the poisonous CO_ads in between.     

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.     

Structural dependence of hydrogen evolution reaction on transition metal catalysts sputtered at different temperatures in alkaline media

In the present article, we studied the catalytic activity of magnetron sputtered Mo, V, Ni, and Co thin films for hydrogen evolution reaction (HER) in the alkaline electrolyte. We find that the HER potentials (η₁₀) of the Mo and V thin film catalysts sputtered at 800 °C shift positive with respect to those of the film catalysts sputtered at 25 °C. For Mo metal the observed shift of η₁₀ was 280 mV and for V metal observed shift of η₁₀ was 390 mV. On the other hand, minimal effect of sputtering temperature on both Ni and Co thin film catalyst activity for HER was observed. Structural analysis reveals that Mo and V prepared at 800 °C have uncommon face centered cubic (fcc, 0.74 packing density) structure as opposed to room-temperature sputtered Mo and V thin films which have common body centered cubic (bcc, 0.68 packing density) structure, resulting in significant increases of the packing densities when they are prepared at 800 °C. On the other hand, the high-temperature prepared thin films of Ni and Co retained fcc structures, resulting in no density changes compared to the room-temperature prepared fcc Ni and hexagonal close packed (hcp, 0.74 packing density) Co. Impedance spectroscopy shows that fcc Mo is a better catalyst than fcc Ni, which is considered an industry standard for non-noble pure metal-based catalysts in alkaline media. Stability tests also suggest that fcc Mo thin film catalysts prepared at 800 °C are more durable than fcc Ni thin films. Our study points out that structure phases of catalysts can be a key factor governing the activities of transition metals for HER in alkaline media.     

PtM/C (M = Sn,Ru, Pd,W) based anode direct ethanol–PEMFCs: Structural characteristics and cell performance

In the present work, the role of the structural characteristics of Pt-based catalysts on the single direct ethanol proton exchange membrane fuel cell (PEMFC) performance is examined. Several PtM/C (M = Sn, Ru, Pd, W) catalysts were characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) and then evaluated as anode catalysts in single direct ethanol fuel cells. XRD spectra showed that Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. According to the obtained experimental results, PtSn catalysts presented better electrocatalytic activity towards ethanol electro-oxidation. Based on these results, PtSn/C catalysts with different Pt/Sn atomic ratio were tested and compared. The maximum power density values obtained were correlated with the structural characteristics of the catalysts. A volcano type behaviour between the fuel cell maximum power density and the corresponding atomic percentage of Sn (Sn%) was observed. It was also observed that Sn% affects almost linearly the Pt_xSn_y catalysts’ lattice parameter.     

Top-down preparation of Ni–Pd–P@graphitic carbon core-shell nanostructure as a non-Pt catalyst for enhanced electrocatalytic reactions

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni₂P and PdP₂) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm^?2 in the OER, high specific activity (2.82 mA cm^?2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg^?1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.     

Pd nanoparticles supported on ultrahigh surface area honeycomb-like carbon for alcohol electrooxidation

The honeycomb-like porous carbon was prepared using glucose as carbon source and solid core mesoporous shell (SCMS) silica as templates. The material was characterized by physical and electrochemical methods. The results showed that the honeycomb-like porous carbon was consisted of hollow porous carbon (HPC) which gave an ultrahigh BET surface area of 1012.97 m² g⁻¹ and pore volume of 2.19 cm³ g⁻¹. The porous walls of the HPC were formed in the mesoporous shells of the silica templates. The HPC was used as the support to load Pd nanoparticles (Pd/HPC) for alcohol electrooxidation. It was highly active for methanol, ethanol and isopropanol electrooxidation. The peak current density for ethanol electrooxidation on Pd/HPC electrode was five times higher than that on Pd/C electrode at the same Pd loadings. The mass activity for ethanol electrooxidation was 4000 A g⁻¹ which is much higher compared to the data reported in the literature. The highly porous structure of such HPC can be widely used as support for uniform dispersing metal nanoparticles to increase their utilization as electrocatalysts.