Enhanced CO Tolerance Research Articles

Growth Modulation of High-Entropy Alloys for Electrocatalytic Methanol Oxidation Reaction.

High-entropy alloy (HEA) electrocatalysts have exhibited remarkable catalytic performance because of their synergistic interactions among multiple metals. However, the growth mechanism of HEAs remains elusive, primarily due to the constraints imposed by the current synthesis methodologies for HEAs. In this work, an innovative electrodeposition method was developed to fabricate Pt-based nanocomposites (Pt1Bi2Co1Cu1Ni1/CC), comprising HEA nanosheets and carbon cloths (CCs). The reaction system could be effectively monitored by taking samples out from the system during the reaction process, facilitating in-depth insight into the growth mechanism underlying the material formation. In particular, Pt1Bi2Co1Cu1Ni1/CC nanocomposites show superior methanol oxidation reaction (MOR) performance (mass activity up to 5.02 A mgPt-1). Upon structural analysis, the d-band center of Pt1Bi2Co1Cu1Ni1/CC is lower in comparison with that of Pt1Bi2/CC and Pt/CC, demonstrating the formation of a rich-electron structure. Both the uniformity of HEAs and the carbon-supported effect could provide additional active sites. These findings suggest that the strong electronic interaction within HEAs and additional active sites can effectively modulate the catalytic structure of Pt, which benefits the enhanced CO tolerance and MOR performance.

Mo-modified Pt/C electrocatalyst prepared by the catalytic decomposition of molybdenum peroxo-complexes for the hydrogen oxidation reaction with enhanced CO tolerance

Commercial 20 % Pt/C catalyst was modified by molybdenum via catalytic decomposition of peroxocomplexes of molybdenum with the subsequent reduction of the Pt2Mo1/C precursor in H2 flow at 600 °C. The detailed HRTEM, EDX, XRD and XPS studies showed that amorphous molybdenum oxide was deposited on Pt particles surface and partially on carbon support. After reduction of the Pt2Mo1/C precursor, the substantial Mo fraction merges the structure of Pt particles thus forming PtMo alloy with reduced lattice parameter, while the rest of molybdenum covers the surface of PtMo particles as MoO3. The presented method of Mo-modification of Pt-based catalysts provides rather simple way to vary Pt:Mo molar ratio. Electrochemical study revealed that the amount of the surface MoO3 plays a key role in the CO tolerance of the PtMo/C catalyst. As prepared Pt2Mo1/C precursor is 15 times superior to the Pt/C catalyst in the CO-tolerance. After reduction, the Pt2Mo1/C electrocatalyst exhibits extremely high CO-tolerance, more than 100 times higher than that of the pristine commercial platinum catalyst.

Enhanced carbon monoxide tolerance of platinum nanoparticles synthesized through the Flash Joule Heating Method

Was employ the Flash Joule Heating Method (FJHM) to synthesize carbon-supported Pt nanoparticles. In this method, an aqueous solution of the Pt precursorH2PtCl6·6 H2O is introduced into a reactor containing Vulcan XC 72 carbon. Subsequently, the mixture undergoes 50 cycles of discharges at 100 coulombs per discharge. Comparative XRD analysis with a commercially prepared Pt/C BASF, utilizing a reduction deposition method, reveals an expansion in the interplanar spacing of the platinum crystal lattice in the FJHM-prepared Pt/C catalyst (FJHM-Pt/C). This expansion suggests the emergence of structural defects, a finding confirmed by TEM images displaying distinct step-like features on the FJHM-Pt/C surface. Cyclic voltammogram analysis demonstrates a noteworthy increase in the oxidation pre-peak at 0.5 V for FJHM-Pt/C compared to Pt/C BASF. When employing pure H2 as fuel, the single proton exchange membrane fuel cell (PEMFC) utilizing Pt/C BASF as the anode catalyst exhibits a higher maximum power density (MPD) than its FJHM-Pt/C counterpart. Conversely, in the presence of CO, the PEMFC with FJHM-Pt/C as the catalyst demonstrates a superior MPD compared to the cell equipped with commercial Pt/C as the anode. These findings underscore enhanced CO tolerance, highlighting the potential advantages of the FJHM preparation method.

Enhanced CO Tolerance with PtRuAuPd/C Anode Catalyst in Proton Exchange Membrane Fuel Cells

Enhanced CO Tolerance with PtRuAuPd/C Anode Catalyst in Proton Exchange Membrane Fuel Cells

Mixed-Dimensional Partial Dealloyed PtCuBi/C as High-Performance Electrocatalysts for Methanol Oxidation with Enhanced CO Tolerance.

Developing efficient electrocatalysts for methanol oxidation reaction (MOR) is crucial in advancing the commercialization of direct methanol fuel cells (DMFCs). Herein, carbon-supported 0D/2D PtCuBi/C (0D/2D PtCuBi/C) catalysts are fabricated through a solvothermal method, followed by a partial electrochemical dealloying process to form a novel mixed-dimensional electrochemically dealloyed PtCuBi/C (0D/2D D-PtCuBi/C) catalysts. Benefiting from distinctive mixed-dimensional structure and composition, the as-obtained 0D/2D D-PtCuBi/C catalysts possess abundant accessible active sites. The introduction of Cu as a water-activating element weakens the COads, and oxophilic metal Bi facilitates the OHads, thereby enhancing its tolerance to CO poisoning and promoting MOR activity. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS) collectively reveal the electron transfer from Cu and Bi to Pt, the electron-enrichment effect induced by dealloying, and the strong interactions among Pt-M (Cu, Pt, and Bi) multi-active sites, which improve the tuning of the electronic structure and enhancement of electron transfer ability. Impressively, the optimized 0D/2D D-PtCuBi/C catalysts exhibit the superior mass activity (MA) of 17.68 A mgPt -1 for MOR, which is 14.86 times higher than that of commercial Pt/C. This study offers a proposed strategy for Pt-based alloy catalysts, enabling their use as efficient anodic materials in fuel cell applications.

Bismuth Incorporation in Palladium Hydride for the Electrocatalytic Ethanol Oxidation with Enhanced CO Tolerance.

Introducing nonmetal and oxophilic metal into palladium (Pd)-based catalysts is beneficial for boosting electrocatalysis, especially regarding the improvement of mass activity (MA) and CO tolerance. Herein, the stable bismuth-doped palladium hydride (Bi/PdH) networks have been successfully fabricated through a simple one-step method. The intercalation of interstitial H atoms expands the lattice of Pd, and the doping of oxophilic metal Bi restrains the adsorption of poisonous intermediates on the surface of Pd, thereby improving the activity and durability of the as-prepared catalysts in the ethanol oxidation reaction (EOR). The obtained Bi/PdH networks manifest a remarkable MA of 8.51 A·mgPd-1, which is 11.18 times higher than that of commercial Pd/C (0.76 A·mgPd-1). The CO-stripping analysis results indicate that Bi doping can significantly prohibit CO adsorption on the surface of the Bi/PdH networks. The density functional theory (DFT) calculations also reveal that Bi doping enhances the OH* adsorption on the catalyst surface and mitigates the interaction between Pd and CO* intermediates, providing deeper insights into the origin of the enhanced EOR activity and CO tolerance. This work describes an impactful path for producing high-performance and durable PdH-based nanocatalysts.

Formicary-like PtBi1.5Ni0.2Co0.2Cu0.2 high-entropy alloy aerogels as an efficient and stable electrocatalyst for methanol oxidation reaction

High-entropy alloy aerogels (HEAAs) have become promising electrochemical catalysts because of the advantageous combination of high-entropy alloys and aerogel structure. However, how to fabricate 3D porous high-entropy alloys accurately is still a great challenge due to their inherent thermodynamic instability and differences in reduction potentials of metal ions. Herein, PtBi1.5Ni0.2Co0.2Cu0.2 HEAAs have been synthesized by combining co-reduction method and freeze-drying technology. The resulting PtBi1.5Ni0.2Co0.2Cu0.2 HEAAs have the structural and morphological benefits of both high-entropy alloys and aerogels. Both XPS and DFT results confirm that the d-band center of PtBi1.5Ni0.2Co0.2Cu0.2 HEAAs shifts to lower binding energy compared to Pt/C, indicating the effective regulation of electronic structure on the surface of PtBi1.5Ni0.2Co0.2Cu0.2 HEAAs. As a demonstration in the methanol oxidation reaction (MOR), a mass activity of 4.19 A mgPt−1 and long-term stability (>0.33 A mgPt−1 after 10 cycles of 3600 s stability test) can be obtained on the PtBi1.5Ni0.2Co0.2Cu0.2 HEAAs, outperforming binary Pt-based alloys and commercial Pt/C. The CO adsorption strength of PtBi1.5Ni0.2Co0.2Cu0.2 HEAAs is more weaker than that of PtBi1.5 alloys and Pt/C, which proves the enhanced CO tolerance. The results pave the way for fabricating the hybrids of high-entropy alloys and aerogels with superior activity and stability.

Embedding oxophilic rare-earth single atom in platinum nanoclusters for efficient hydrogen electro-oxidation

Designing Pt-based electrocatalysts with high catalytic activity and CO tolerance is challenging but extremely desirable for alkaline hydrogen oxidation reaction. Herein we report the design of a series of single-atom lanthanide (La, Ce, Pr, Nd, and Lu)-embedded ultrasmall Pt nanoclusters for efficient alkaline hydrogen electro-oxidation catalysis based on vapor filling and spatially confined reduction/growth of metal species. Mechanism studies reveal that oxophilic single-atom lanthanide species in Pt nanoclusters can serve as the Lewis acid site for selective OH- adsorption and regulate the binding strength of intermediates on Pt sites, which promotes the kinetics of hydrogen oxidation and CO oxidation by accelerating the combination of OH− and *H/*CO in kinetics and thermodynamics, endowing the electrocatalyst with up to 14.3-times higher mass activity than commercial Pt/C and enhanced CO tolerance. This work may shed light on the design of metal nanocluster-based electrocatalysts for energy conversion.

Unconventional Bilateral Compressive Strained Ni-Ir Interface Synergistically Accelerates Alkaline Hydrogen Oxidation.

The alkaline hydrogen oxidation reaction (HOR) involves the coupling of adsorbed hydrogen (Had) and hydroxyl (OHad) species and is thus orders of magnitude slower than that in acid media. According to the Sabatier principle, developing electrocatalysts with appropriate binding energy for both intermediates is vital to accelerating the HOR though it is still challenging. Herein, we propose an unconventional bilateral compressive strained Ni-Ir interface (Ni-Ir(BCS)) as efficient synergistic HOR sites. Density functional theory (DFT) simulations reveal that the bilateral compressive strain effect leads to the appropriate adsorption for both Had and OHad, enabling their coupling thermodynamically spontaneous and kinetically preferential. Such Ni-Ir(BCS) is experimentally achieved by embedding sub-nanometer Ir clusters in graphene-loaded high-density Ni nanocrystals (Ni-Ir(BCS)/G). As predicted, it exhibits a HOR mass activity of 7.95 and 2.88 times those of commercial Ir/C and Pt/C together with much enhanced CO tolerance, respectively, ranking among the most active state-of-the-art HOR catalysts. These results provide new insights into the rational design of advanced electrocatalysts involving coordinated adsorption and activation of multiple reactants.

Electrodeposition of CoNi Cocatalyst to Enhance Ethanol Electrooxidation of Zn-doped Cu2O-Cu Photocatalyst

In this research, the electrooxidation of ethanol was catalyzed using Zn-doped Cu2O-Cu/CoNi heterostructure syntesized using an electrodeposition method. Potential deposition of CoNi cocatalyst was varied to obtain the highest photoelectrochemical performance and photocatalytic activity of Zn-doped Cu2O-Cu/CoNi. The photoelectrochemical properties and photocatalytic activity investigated by electrochemical impedance spectroscopy, linear sweep voltammetry, and cyclic voltammetry. The increase of deposition potential from -1.3 V to -1.75 V increased the ethanol oxidation reaction. Zn-doped Cu2O-Cu/CoNi -1.75 V electrode showed superior photocatalytic activity for the ethanol electrooxidation compared to other electrodes. This photocatalyst showed a high photocurrent density of 22.47 mA/cm2. Moreover, cyclic voltammetry tests up to 100 cycles indicated that CoNi deposition potential at -2 V increased the long-term stability of the photocatalyst against the poisoning species than other electrodes. The fraction of CoNi enhanced CO tolerance and contributed to the higher specific activity towards ethanol electrooxidation. An excess number of CoNi at -2 V was found to decrease photocatalytic activity but increase the photostability of the material.

Self-catalytic induced interstitial C-doping of Pd nanoalloys for highly selective electrocatalytic dehydrogenation of formic acid

Light-metalloid-atom-doped Pd interstitial nanoalloy is promising candidate for electrocatalysis because of the favorable electronic effect. Herein, an innovative method was developed to synthesize C-doped Pd interstitial nanoalloy using palladium acetate both as metal precursor and C dopant. Elaborate characterizations demonstrated that C atoms were successfully doped into the Pd lattice via self-catalytic decomposition of acetate ions. The as-synthesized C-doped Pd catalysts showed excellent activity and durable stability for formic acid electrooxidation. The mass activity and specific activity at 0.6 V of C-doped Pd were approximately 2.59 A/mg and 3.50 mA cm−2, i.e., 2.4 and 2.6 times of Pd, respectively. DFT calculations revealed that interstitial doping with C atoms induced differentiation of Pd sites. The strong noncovalent interaction between the Pd sites and the key intermediates endowed Pd with high-selectivity to direct routes and enhanced CO tolerance. This work presents a sites-differentiation strategy for metallic catalysts to improve the electrocatalysis.

Highly active Pt/In2O3-ZrO2 catalyst for CO2 hydrogenation to methanol with enhanced CO tolerance: The effects of ZrO2

The supported Pt catalyst is normally not active for CO2 hydrogenation to methanol at the presence of CO. Herein, ZrO2 is added into Pt/In2O3 for CO2 hydrogenation to methanol with CO as a co-feed gas. High activity with enhanced CO tolerance is achieved on Pt/In2O3-ZrO2. For example, the space-time yield of methanol reaches 0.569 gmethanol gcat−1 h−1 at 300 °C and 5 MPa under feed gas containing 4% CO of 21,000 cm3·h−1·gcat−1. With the addition of ZrO2, a stronger electron transfer occurs between Pt and the In2O3-ZrO2 solid solution support. This leads to weaker CO adsorption, which suppresses over-reduction of In2O3 and enhances CO tolerance of the Pt catalyst. The oxygen vacancy of In2O3 modified by ZrO2 promotes CO2 activation. The synergy between Zr-modified oxygen vacancy (In-Ov-Zr) and Pt catalyst facilitates methanol synthesis from CO2 hydrogenation via formate route. This is different from Pt/In2O3, which takes CO hydrogenation route.

Preparation of Pt electrocatalyst supported by novel, Ti(1\u2212x)MoxO2-C type of composites containing multi-layer graphene

Ball milling is a relative simple and promising technique for preparation of inorganic oxide–carbon type of composites. Novel TiO2-C and Ti0.8Mo2O2-C type of composites containing multi-layer graphene were prepared by ball milling of graphite in order to get electrocatalyst supports for polymer electrolyte membrane fuel cells. Starting rutile TiO2 was obtained from P25 by heat treatment. Carbon-free Ti0.8Mo2O2 mixed oxide, prepared using our previously developed multistep sol–gel method, does not meet the requirements for materials of electrocatalyst support, therefore parent composites with Ti0.8Mo2O2/C = 75/25, 90/10 and 95/5 mass ratio were prepared using Black Pearls 2000. XRD study of parent composites proved that the oxide part existed in rutile phase which is prerequisite of the incorporation of oxophilic metals providing CO tolerance for the electrocatalyst. Ball milling of TiO2 or parent composites with graphite resulted in catalyst supports with enhanced carbon content and with appropriate specific surface areas. XRD and Raman spectroscopic measurements indicated the changes of graphite during the ball milling procedure while the oxide part remained intact. TEM images proved that platinum existed in the form of highly dispersed nanoparticles on the surface of both the Mo-free and of Mo-containing electrocatalyst. Electrocatalytic performance of the catalysts loaded with 20 wt% Pt was studied by cyclic voltammetry, COads-stripping voltammetry done before and after the 500-cycle stability test, as well as by the long-term stability test involving 10,000 polarization cycles. Enhanced CO tolerance and slightly lower stability comparing to Pt/TiO2-C was demonstrated for Pt/Ti0.8Mo2O2-C catalysts.

A highly-efficient and durable Pt-based electrocatalyst decorated by Co2C-Mo2C@CS composite for methanol oxidation reaction

Designing highly efficient electrocatalysts for the methanol electro-oxidation is an ongoing challenge. Herein, we report that molybdenum carbide (Mo2C) and cobalt carbide (Co2C) are grown in situ on the surface of carbon spheres to form Co2C-Mo2C@CS carrier material by the impregnation-reduction-annealing process, and then Pt nanoparticles are deposited on the Co2C-Mo2C@CS surface through sodium borohydride reduction method. In-depth material characterizations and electrochemical analyses demonstrate that the introduction of small-sized Mo2C-Co2C composites can facilitate mass transfer and increase the solid-liquid interface area. As expected, the resulting Pt/Co2C-Mo2C@CS catalyst displays excellent methanol oxidation activity (1504.5 mA mgPt−1), enhanced CO tolerance and stability comparing with other catalysts, which mainly derived from the metal-support interaction between Co2C-Mo2C and small-sized Pt NPs. The rational design of Pt/Co2C-Mo2C@CS catalyst provides a feasible strategy for boosting the overall performance of Pt-based catalysts towards methanol oxidation, and broadens the potential applications of metal carbides.

Effects of CeO2 pre-calcined at different temperatures on the performance of Pt/CeO2-C electrocatalyst for methanol oxidation reaction

Pt/CeO2-C catalysts with CeO2 pre-calcined at 300–600°C were synthesized by combining hydrothermal calcination and wet impregnation. The effects of the pre-calcined CeO2 on the performance of Pt/CeO2-C catalysts in methanol oxidation were investigated. The Pt/CeO2-C catalysts with pre-calcined CeO2 at 300–600°C showed an average particle size of 2.6–2.9 nm and exhibited better methanol electro-oxidation catalytic activity than the commercial Pt/C catalyst. In specific, the Pt/CeO2-C catalysts with pre-calcined CeO2 at 400°C displayed the highest electrochemical surface area value of 68.14 m2·g−1 and If/Ib ratio (the ratio of the forward scanning peak current density (If) and the backward scanning peak current density (Ib)) of 1.26, which are considerably larger than those (53.23 m2·g−1 and 0.79, respectively) of the commercial Pt/C catalyst, implying greatly enhanced CO tolerance.

Preparation of CO-tolerant PtRuNi/C ternary electrocatalyst having a composition gradient shell

The carbon-supported PtRuNi/C ternary electrocatalyst having a composition gradient shell was developed using the high-temperature heat treatment and polydopamine protective coating techniques. The fabricated catalyst is a CO-tolerant anode catalyst developed for use in polymer electrolyte membrane fuel cells (PEMFCs). Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy techniques were used to characterize the catalyst. The results revealed that high-temperature heat treatment led to atomic rearrangement in the shell, resulting in increased Pt content on the catalyst surface and an increased ratio of Ru and Ni in order. The Pt and Ru layers effectively prevent Ni leaching in the acidic environment of the PEMFCs. In addition, a protective coating of polydopamine suppresses the sintering of the catalyst particles when the high-temperature treatment technique is used for catalyst fabrication, thereby preventing the decrease of the active surface area of the catalyst. As a result of the change in the electronic structure of Pt induced by the underlying Ru and Ni atoms, the PtRuNi/C catalyst exhibited enhanced CO tolerance compared to the Pt/C and PtRu/C catalysts as proved by the results from the CO stripping voltammetry and PEMFC test.

Alloyed Palladium–Silver Nanowires Enabling Ultrastable Carbon Dioxide Reduction to Formate

Palladium can enable the electrochemical CO2 reduction to formate with nearly zero overpotential and good selectivity. However, it usually has very limited stability owing to CO poisoning from the side reaction intermediate. Herein, it is demonstrated that alloying palladium with silver is a viable strategy to significantly enhance the electrocatalytic stability. Palladium-silver alloy nanowires are prepared in aqueous solution with tunable chemical compositions, large aspect ratio, and roughened surfaces. Thanks to the unique synergy between palladium and silver, these nanowires exhibit outstanding electrocatalytic performances for selective formate production. Most remarkably, impressive long-term stability is measured even at < -0.4V versus reversible hydrogen electrode where people previously believed that formate cannot be stably formed on palladium. Such stability results from the enhanced CO tolerance and selective stabilization of key reaction intermediates on alloy nanowires as supported by detailed electrochemical characterizations and theoretical computations.

Reformate gas composition and pressure effect on CO tolerant Pt/Ti0.8Mo0.2O2–C electrocatalyst for PEM fuel cells

Mixed-oxide coated Ti0.8Mo0.2O2–C composite supported 20 wt% Pt electrocatalysts with Ti0.8Mo0.2O2/C=75/25 mass ratio were developed for CO tolerance of polymer electrolyte membrane fuel cell (PEMFC) anode. Studies of the structure, composition and stability, as well as the results of COads stripping confirmed that the mixed oxide composite support and the electrocatalyst prepared for this study show the well-documented characteristics of the Pt/Ti1-xMoxO2-C systems with enhanced CO tolerance compared to the Pt/C catalyst.Dilution of hydrogen with CO2 and CH4 had negligible negative impact on the fuel cell performance. Switching gas composition between hydrogen and reformate shows recovery of potential after CO poisoning. Nevertheless, anode catalyst loading of 0.25 and 0.5 mgPt/cm2 was not enough to give reasonable performance when CO impurity was present. Loading of 0.85 mgPt/cm2 Ti0.8Mo0.2O2–C supported catalyst was effective to give 1000 mA/cm2 current density at 0.6 V under 25 ppm CO and 30 psig. Higher loading was needed at mass transfer limited region to overcome poisoning. However, loadings higher than 0.85 mgPt/cm2 caused mass transfer limitations. Hence higher loadings is proposed with 40 wt% Pt/Ti0.8Mo0.2O2–C support catalyst.

Enhanced CO tolerance of Pt clusters supported on graphene with lattice vacancies

The adsorption of CO on ${\mathrm{Pt}}_{4}$ clusters supported on graphene with lattice vacancies is studied theoretically using the first-principles calculation. Our results show that the electronic structure of the graphene-supported ${\mathrm{Pt}}_{4}$ clusters is significantly modified by the interaction with carbon dangling bonds. As a result the adsorption energy of CO at a Pt site decreases almost linearly with the lowering of the Pt $d$-band center, in analogy with the linear law previously reported for CO adsorption on various Pt surfaces. An exceptional behavior is found for ${\mathrm{Pt}}_{4}$ supported on graphene with a tetravacancy, where CO adsorption is noticeably weaker than predicted by the shift in the $d$-band center. Detailed electronic structure analyses reveal that the deviation from the linear scaling can be attributed to lack of Pt $d$ states near the Fermi level that hybridize with CO molecular orbitals. The weakening of CO adsorption on the ${\mathrm{Pt}}_{4}$ clusters is considered as a manifestation of the support effect of graphene, and leads to the enhancement of CO poisoning tolerance that is crucial for developing high-performance Pt cluster catalysts.

Surface elemental distribution effect of Pt-Pb hexagonal nanoplates for electrocatalytic methanol oxidation reaction

Bimetallic Pt-based catalysts have been extensively investigated to enhance the performance of direct methanol fuel cells (DMFCs) because CO, a by-product, reduces the activity of the pure Pt catalysts. Herein, we synthesized Pt-Pb hexagonal nanoplates as a model catalyst for the methanol oxidation reaction (MOR) and further controlled the Pt and Pb distributions on the surface of the nanoplates through acetic acid (HAc) treatment. As a result, we obtained Pt-Pb nanoplates and HAc-treated Pt-Pb nanoplates with homogeneous and heterogeneous distributions of the Pt-Pb alloy surfaces, respectively. We showed that the MOR activity and stability of the Pt-Pb nanoplates improved compared to those of the HAc-treated Pt-Pb nanoplates, mainly due to the enhanced CO tolerance and the modified electronic structure of Pt under the influence of the oxophilic Pb.