PtNi Alloy Catalyst Research Articles

Post mortem Study of Catalyst Degradations Occurring in High-Temperature Proton Exchange Membrane Fuel Cells Upon Start-Stop Operation

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) could replace fossil fuel-based technologies for applications which cannot involve bulky/heavy cooling systems, such as aeronautics. However, severe materials degradations upon operation prevent performance retention for acceptable lifetimes. While others have already reported degradations in HT-PEMFC, post mortem characterizations of used HT-PEMFC membrane electrode assemblies (MEAs) remain scarce. Herein, HT-PEMFC performance degradation is studied by applying a startup/shutdown protocol to a short-stack operated at 160 °C; one MEA is characterized using complementary physicochemical/electrochemical techniques to identify/understand the degradation mechanisms and their origin. This start/stop operation mode (co-flow gas reactants) leads to substantial degradation inhomogeneity. For the anode, migration, coalescence, and detachment of Pt nanoparticles are witnessed induced by high-surface-area carbon support functionalization and corrosion. The anode electrochemical surface area (ECSA) remains constant at the inlet and increases significantly at the outlet, following inhomogeneous degradation of the cathode catalyst: the Ptz+ ions formed at high potential/oxidizing conditions concentrate towards the outlet, where they redeposit locally or at the anode, after diffusion/migration across the PBI membrane. Hence, the cathode ECSA decreases significantly at the inlet. Furthermore, intense Ni-leaching from the initial PtNi alloy catalyst is reported as a result of O2 mass-transport and phosphoric acid dilution inhomogeneity.

Synthesis and electrocatalytic evaluation of PtNi catalyst supported on SBA-15 modified carbon

Maximizing catalyst activity and stability while minimizing costs remains a formidable challenge. In this study, we employed the straightforward and easily executed ethylene glycol reduction method to synthesize highly active and stable Pt-Ni alloy catalysts, utilizing SBA15-modified carbon as the supporting material. Subsequent meticulous examinations delved into their physicochemical properties and electrocatalytic activities.Transmission electron microscopy (TEM) analyses unveiled a uniform distribution of PtNi particles on the support, showcasing a narrow particle size distribution centered around approximately 1.91 nm with minimal aggregation. Electrochemical assessments demonstrated that Pt3Ni/SBA15-C outperforms Pt/C, exhibiting 56 and 167 mV higher half-wave potentials (E1/2) and onset potential (Eonset), respectively. Furthermore, our meticulously prepared Pt3Ni/SBA15-C, featuring a cage structure, displayed remarkable stability while sustaining superior catalytic durability under an applied potential of +0.7 V. These findings underscore the effectiveness of the cage structure catalyst, comprising porous nanoparticles, in ensuring both catalytic activity and stability. The results collectively contribute to advancing our understanding of catalyst design and performance optimization in electrochemical applications.

Identifying the distinct roles of dual dopants in stabilizing the platinum-nickel nanowire catalyst for durable fuel cell

Stabilizing active PtNi alloy catalyst toward oxygen reduction reaction is essential for fuel cell. Doping of specific metals is an empirical strategy, however, the atomistic insight into how dopant boosts the stability of PtNi catalyst still remains elusive. Here, with typical examples of Mo and Au dopants, we identify the distinct roles of Mo and Au in stabilizing PtNi nanowires catalysts. Specifically, due to the stronger interaction between atomic orbital for Ni-Mo and Pt-Au, the Mo dopant mainly suppresses the outward diffusion of Ni atoms while the Au dopant contributes to the stabilization of surface Pt overlayer. Inspired by this atomistic understanding, we rationally construct the PtNiMoAu nanowires by integrating the different functions of Mo and Au into one entity. Such catalyst assembled in fuel cell cathode thus presents both remarkable activity and durability, even surpassing the United States Department of Energy technical targets for 2025.

Solution-plasma interaction for synthesizing highly active Pt-Ni alloy oxygen reduction nanocatalysts for PEMFCs.

A highly active PtNi-alloy catalyst (p-PtNi/KB) is synthesized using solution-plasma interaction. The plasma effect results in a substantial increase of active sites on the support surface. This facilitates the alloying and functionalization of supports, enabling achievement of enhanced catalytic activity and effective resolution of cost-related challenges in fuel cells.

Electrochemical Ethylamine Dehydrogenation to Acetonitrile on Platinum-Based Catalysts

Hydrogen storage is a crucial link between green hydrogen generation by water electrolysis and hydrogen application in fuel cells. We very recently reported a new, electrochemical ethylamine/acetonitrile redox method for hydrogen storage [1]. This method realizes hydrogen uptake by pairing acetonitrile hydrogenation to ethylamine reaction (AHR) on cathode and hydrogen oxidation reaction (HOR) on anode, and realizes hydrogen release by pairing ethylamine dehydrogenation to acetonitrile reaction (EDR) on anode and hydrogen evolution reaction (HER) on cathode. With 8.9 wt.% theoretical storage capacity and ambient reaction conditions being demonstrated in the study, this method shows a great potential to advance hydrogen storage technology and meet the DOE target. One remaining challenge of this method was a rapid activity decay of the used commercial platinum catalyst (Pt/C) in the EDR, which caused a long-term durability issue.In this work, we report our fundamental study of Pt catalyst deactivation mechanism in EDR and the discovery of new Pt-based catalysts. Attenuated total reflection infrared spectroscopy (ATR-IR) was employed for characterizing working catalyst surface under reactive conditions. Partially dehydrogenated intermediate species were observed to generate on Pt surface, which strongly adsorbed and caused an accumulation and blockage of the active sites. Interestingly, the catalyst showed a self-cleaning property where the intermediates can be hydrogenated back to ethylamine and released from Pt surface below 0 V vs. RHE. A group of Pt-Ni alloy catalysts were prepared and investigated the composition effect in this reaction, among which Pt3Ni exhibited 75% higher activity and significantly improved stability compared to Pt. ATR-IR experiments showed that the accumulation of intermediates on the Pt3Ni surface was much slower than that on the Pt, attributed to weakened adsorption. This work provides mechanistic insights into EDR reaction pathways and the cause of Pt catalyst deactivation and offers a Pt alloy strategy for active and stable catalyst design.[1] Wu, D.; Li, J.; Yao, L.; Xie, R.; Peng, Z. ACS Appl. Mater. Interfaces 13, 55292 (2021).

Efficient Hydrogenation of Glucose to Polyols over Hydrotalcite-Derived PtNi Alloy Catalyst under Mild Conditions

Polyols are important biomass-based building blocks for chemical production. In this work, a hydrotalcite-derived PtNi alloy catalyst (PtNi/HT) was prepared with high metal dispersion under microwave-assisted synthesis and employed for glucose hydrogenation, where 95.7% of glucose was converted with 90.1% selectivity into polyols at 393 K in water. The PtNi/HT was stable and could be recycled for at least five runs for glucose. Lower reaction temperatures (333–373 K) contributed to glucose hydrogenation to hexitols, while higher reaction temperatures (373–413 K) facilitated the C–C activation of glucose to generate more polyols with less carbon (C2–C4). The Ptδ−–Niδ+ pair on PtNi/HT contributed to both H2 activation and adsorption of the aldehyde group in glucose hydrogenation. The basic support of PtNi/HT can efficiently catalyze the glucose isomerization and retro-aldol reaction in the aqueous phase. This study advocates a green approach for sustainable biorefinery of readily available glucose into value-added chemicals.

Nanostructure Engineering and Electronic Modulation of a PtNi Alloy Catalyst for Enhanced Oxygen Reduction Electrocatalysis in Zinc-Air Batteries.

PtNi nanoalloys have demonstrated electrocatalysis superior to that of benchmark Pt/C catalysts for the oxygen reduction reaction (ORR), yet the underlying mechanisms remain underexplored. Herein, a PtNi/NC catalyst comprising PtNi nanoparticles (∼5.2 nm in size) dispersed on N-doped carbon frameworks was prepared using a simple pyrolysis strategy. Benefiting from the individual components and a hierarchical structure, the PtNi/NC catalyst exhibited outstanding ORR activity and stability (E1/2 = 0.82 V vs RHE and 8 mV negative shift after 20000 cycles), outperforming a commercial 20 wt % Pt/C catalyst (E1/2 = 0.81 V and 32 mV negative shift). A prototype zinc-air battery constructed using PtNi/NC as the air electrode catalyst achieved highly enhanced electrochemical performance, outperforming a battery constructed using Pt/C as the ORR catalyst. Density functional theory calculations revealed that the improved ORR activity of the PtNi nanoalloys originated from charge redistribution with a suitable metal d-band center to promote the formation of the ORR intermediates.

Oxygen Reduction at PtNi Alloys in Direct Methanol Fuel Cells—Electrode Development and Characterization

Catalyst layers made from novel catalysts must be fabricated in a way that the catalyst can function to its full potential. To characterize a PtNi alloy catalyst for use in the cathode of Direct Methanol Fuel Cells (DMFCs), the effects of the manufacturing technique, ink composition, layer composition, and catalyst loading were here studied in order to reach the maximum performance potential of the catalyst. For a more detailed understanding, beyond the DMFCs performance measurements, we look at the electrochemically active surface area of the catalyst and charge-transfer resistance, as well as the layer quality and ink properties, and relate them to the aspects stated above. As a result, we make catalyst layers with optimized parameters by ultrasonic spray coating that shows the high performance of the catalyst even when containing less Pt than commercial products. Using this approach, we can adjust the catalyst layers to the requirements of DMFCs, hydrogen fuel cells, or polymer electrolyte membrane electrolysis cells.

Low-Pt NiNC-Supported PtNi Nanoalloy Oxygen Reduction Reaction Electrocatalysts-In Situ Tracking of the Atomic Alloying Process.

We report and analyze a synthetic strategy toward low‐Pt platinum‐nickel (Pt‐Ni) alloy nanoparticle (NP) cathode catalysts for the catalytic electroreduction of molecular oxygen to water. The synthesis involves the pyrolysis and leaching of Ni‐organic polymers, subsequent Pt NP deposition, followed by thermal alloying, resulting in single Ni atom site (NiNC)‐supported PtNi alloy NPs at low Pt weight loadings of only 3–5 wt %. Despite low Pt weight loading, the catalysts exhibit more favorable Pt‐mass activities compared to conventional 20–30 wt % benchmark PtNi catalysts. Using in situ microscopic techniques, we track and unravel the key stages of the PtNi alloy formation process directly at the atomic scale. Surprisingly, we find that carbon‐encapsulated metallic Ni@C structures, rather than NiN x sites, act as the Ni source during alloy formation. Our materials concepts offer a pathway to further decrease the overall Pt content in hydrogen fuel cell cathodes.

Ni-MOF with Dual Organic Ligands Derived Pt-Ni Alloy Catalyst for Highly Efficient Hydrogen Evolution Reaction

Abstract N-doped carbon-modified carbon nanotube/Pt-Ni alloy catalysts were prepared via a thermal decomposition of Ni-MOF with dual organic ligands (triethylene diamine and terephthalic acid). Different from the individual Pt and Ni nanoparticles derived from Ni-MOF with a single organic ligand, the dual organic ligands bestow the obtained Pt-Ni nanoparticles with alloy structure. The fabricated catalyst exhibits significant hydrogen evolution reaction activity and stability in the alkaline solution, with an overpotential of −196 mV to achieve 10 mA cm−2. Moreover, the TOF value of CNT/Pt-Ni catalyst is 2.1 times greater than the incumbent commercial Pt/C catalyst (at the overpotential of −300 mV), demonstrating it as a promising electrocatalyst for water splitting reaction.

Atomic layer deposition enabled PtNi alloy catalysts for accelerated fuel-cell oxygen reduction activity and stability

Structuring Pt-based alloy catalysts with uniform, dense dispersion, and low loading is a challenging work for efficient and relatively low-cost catalysts to promote oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Herein, we present a strategy of active PtNi alloy structure formation with uniform metal alloy nanoparticles (NPs) using fluidized bed reactor atomic layer deposition (FBR-ALD). The compositions of the PtNi alloys were controlled by the ALD super-cycle method, where Pt75+XNi25-X alloy catalysts were successfully synthesized by tuning the super-cycle ratio. The as-deposited alloy catalysts consisted of well-dispersed and dense metal NPs, whose characteristics were maintained even after heat treatment at 700 °C with H2 to produce a well-mixed PtNi alloy. During heat treatment, the Pt-rich Pt3Ni alloy converted into the Pt skin-Pt3Ni alloy structure from the ALD growth mechanism, which is evidenced by spherical aberration (Cs)-corrected transmission electron microscopy (TEM), line profiling, X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The ALD synthesized Pt skin-Pt3Ni alloy structure featured a significantly higher electrochemical surface area (ECSA) as well as ORR activity, durability, and PEMFC performance compared to the commercial Pt and Pt3Ni catalysts due to their excellent uniformity, density, and well dispersity as well as the Pt skin-Pt3Ni structure. This study focuses on an atomic scale strategy for a new alloy architecture and marks a step toward a modern high-performing alloy catalyst for future PEMFC technology.

High Oxygen Reduction Activity of Pt-Ni Alloy Catalyst for Proton Exchange Membrane Fuel Cells

In order to fill the research gap of high metal loading of high performance PtNi alloy catalysts, a PtNi/C alloy nano-catalyst with metal loading more than 50 wt.% and core-shell like structure was prepared by ethylene glycol reduction, high temperature annealing, and acid pickling. The electrochemical test results showed that the prepared PtNi alloy catalyst had excellent electrochemical activity: the electrochemical surface area (ECSA) was 63.8 m2·gPt−1, and the mass activity (MA) was 0.574 A·mgPt−1, which is 2.73 times greater than those of the Pt/C JM (Johnson Matthey) catalyst. The durability of the PtNi/C catalyst was further investigated. After 30 K cycles of accelerated durability test, the ECSA and MA of the PtNi/C alloy catalyst decreased by 10.2% and 31.2%, respectively. The PtNi/C alloy catalyst prepared in this study has excellent catalytic activity and overcomes the problem of insufficient durability of traditional alloy catalysts and has the potential for large-scale commercial application.

Theoretical insights into the oxygen reduction reaction on PtNi (111): Effects of acidic solvent and Pd-modification

PtNi alloys have been considered as promising electrocatalysts for oxygen reduction reaction (ORR), and the strategies of constructing surface defects and ternary alloys have been adopted to further improve their performance. However, theoretical insights on their ORR catalytic kinetics under realistic acidic conditions, typically including the surface H-covering and presence of hydroxonium, are rarely studied. In this work, the effect of H-coverage and Pd-modification on the ORR reaction kinetics on defective PtNi (111)-DF was systematically investigated by performing density functional theory (DFT) calculations on the H covered H-PtNi (111)-DF, Pd-modified PtNiPd (111) and H-PtNiPd (111) models. The results reveal that ORR on H-PtNi (111)-DF follows the O2 dissociation pathway, and on PtNiPd (111) is H2O2 dissociation pathway. However, when H coverage is considered, on PtNiPd (111), ORR would follow the OOH dissociation pathway with lowest reaction energy barrier among these models. Moreover, it is found that hydroniums in the solvent are instrumental in facilitating the protonation of active surface intermediates, thus promoting the ORR reaction. This work unveils the effect of acidic condition and the Pd introduction on the ORR kinetics of PtNi alloy catalysts.

Pt-Ni alloy catalyst supported on carbon aerogel via one-step method for oxygen reduction reaction

Pt-Ni alloy catalyst supported on carbon aerogel via one-step method for oxygen reduction reaction

Selective Hydrogenation of the Carbonyls in Furfural and 5-Hydroxymethylfurfural Catalyzed by PtNi Alloy Supported on SBA-15 in Aqueous Solution Under Mild Conditions.

Valuable furfuryl alcohol (FFA) and 2,5-dihydroxymethylfuran (DHMF) could be produced by selective hydrogenation of biomass-derived furfural (FF) and 5-hydroxymethylfurfural (HMF) with high atom economy. In this study, SBA-15 (a kind of mesoporous silica molecular sieve)-supported low metal loading (3 wt% total metal content) PtNi alloy catalyst (PtNi/SBA-15) was synthesized via two steps, including the generation of PtNi alloy by hydrothermal method, and the immobilization of PtNi alloy on SBA-15. PtNi/SBA-15 has ordered mesoporous structure with high surface area, and high dispersion of the PtNi alloy with the formation of Ptδ−-Niδ+ surface pairs on SBA-15, which benefit hydrogen activation and selective carbonyl hydrogenation. The selective hydrogenation of FF and HMF over PtNi/SBA-15 in water solvent at 303 K with 1.5 MPa H2 within 2 h, could respectively yield 64.6% FFA with 77.0% selectivity, and 68.2% DHMF with 81.9% selectivity. Besides, PtNi/SBA-15 exhibited a satisfactory water resistance and stability after recycling at least five runs.

Electrochemical modification and structural characterization of porous PtNi/C catalyst

The development of catalysts for high-efficient hydrogen evolution reaction (HER) is important for future sustainable energy conversion. Herein, porous carbon-supported PtNi alloy catalysts were fabricated by ion beam sputtering and ultrasonic-assisted electrochemical corrosion dealloying methods, and their performances toward the catalysis of HER were evaluated. The effects of corrosion dealloying on the hydrogen evolution activity, as well as stability, phase structure, surface composition, and active sites of PtNi alloys were analyzed by various analytical methods combined with orthogonal experiments. The results showed increased catalytic activity of HER by 51.39% after corrosion of the material in 0.2 mol/L H2SO4 at 40 °C for 0.5 h. The hydrogen evolution deteriorated as Pt-loading decreased by 25.83%, and corrosion temperature displayed significant influence. The pore structure of the catalyst surface raised the relative content of the exposed Pt element, and the zero-dimensional defect generated by the Ni atom deletion led to promotion in reaction area and active sites on the catalyst surface. The interplanar spacing of alloys (NiPt) was below 3%−6% of the standard value, and the lattice compressive strain of Pt was the reason that led to improved catalytic performance of PtNi alloy catalysts. The binding energy of the Pt 4f7/2 decreased by 0.74 eV, leading to enhanced electrochemical active sites and promoted hydrogen release.

Molecular Insight of the Critical Role of Ni in Pt-Based Nanocatalysts for Improving the Oxygen Reduction Reaction Probed Using an In Situ SERS Borrowing Strategy.

PtNi alloy catalysts have excellent catalytic activity and are considered some of the most promising electrocatalysts capable of replacing pure Pt for the oxygen reduction reaction (ORR). For PtNi alloys, Ni-doping can improve performance by changing the electronic and structural properties of the catalyst surface and its interaction with reaction intermediates. However, to date there is no direct spectral evidence detecting or identifying the effect of Ni on the ORR in PtNi alloy catalysts. Herein, we introduce a surface-enhanced Raman spectroscopic (SERS) "borrowing" strategy for investigating ORR processes catalyzed by Au@PtNi nanoparticles (NPs). The bond vibration of adsorbed peroxide intermediate species (*OOH) was obtained, and the effect of Ni on the interaction between surface Pt and *OOH was studied by varying the Ni content in the alloy. The frequency of the *OOH spectral band has an obvious red-shift with increasing Ni content. Combined with density functional theory (DFT) calculations, we show that Ni-doping can optimize *OOH surface binding on the Pt surface, achieving more efficient electron transfer, thus improving the ORR rate. Notably, these results evidence the SERS borrowing strategy as an effective technique for in situ observations of catalytic processes.

Preparation of Unique Flower-like Pt-Ni Alloy Catalysts As the Cathode of a PEMFC By Electrodeposition Technique

The hydrogen economy can play an important role in the low-carbon economy, and fuel cells technology is an essential part of the hydrogen economy. The proton exchange membrane fuel cell (PEMFC) is one kind of electrochemical reaction device with the advantages of low temperature operation, high conversion efficiency and noiseless, which is expected to widely utilizes in public transportations.The oxygen reduction reaction (ORR) at the cathode is the rate-determining step in PEMFC. To enhance the ORR activity at the cathode, the unique flower-like platinum-nickel binary alloy catalysts were electrodeposited on the commercial carbon cloth by potentiostatic electrodeposition technique, the PtNi alloy effectively improved the oxygen adsorption and desorption paths on the surface. The PtNi alloy catalysts with shorter lattice distance and effects of high-index facets would increase the electrochemical surface area (ECSA) of the catalysts and power density of fuel cell. The samples of the pure platinum and commercial Pt/C catalyst were also prepared as comparison.Morphology, particle size and elemental composition were characterized by SEM, XRD and ICP-MS. In addition, the electrochemical characteristics of the PtNi catalysts were investigated via cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analysis in 0.1 M perchloric acid solution with rotating disk electrode (RDE). In single cell test, the maximum peak power density of PEMFC with homemade PtNi alloy catalyst as the cathode reached 1031 mW/cm2, enhancing about 12% power density, compared to the commercial Pt/C. Figure 1

Preparation of Unique Flower-like Pt-Ni Alloy Catalysts as the Cathode of a PEMFC by Electrodeposition Technique

The oxygen reduction reaction (ORR) at the cathode is the rate-determining step in a PEMFC. To enhance the ORR activity at the cathode, the unique flower-like platinum-nickel binary alloy catalysts were electrodeposited on the commercial carbon cloth by potentiostatic electrodeposition technique, the PtNi alloy effectively improved the oxygen absorption and desorption paths on the surface. The PtNi binary alloy catalysts with shorter lattice distance and effects of high-index facets would increase the electrochemical surface area (ECSA) of the catalysts and power density of the fuel cell. The samples of the pure platinum and commercial Pt/C catalyst were also prepared as comparison. Morphology, particle size and elemental composition are characterized by SEM, XRD and ICP-MS. In addition, the electrochemical characteristics of the PtNi catalysts were investigated via cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analysis in 0.1 M perchloric acid solution with rotating disk electrode (RDE). In single cell test, the maximum peak power density of PEMFC with homemade PtNi alloy catalyst as the cathode reached 1031 mW/cm2, enhancing about 12% power density, compared to the commercial Pt/C.

Irreversible Structural Dynamics in Bimetallic Pt-Ni Alloy Catalyst Under Alternating Redox Environments

The better understanding on the structural dynamics of a bimetallic catalyst during its interaction with reactive environments is a prerequisite for the development of an efficient catalyst for proton exchange membrane fuel cells (PEMFCs). The main focus should be given to the outermost layers of catalytically active material which are directly involved in catalysis.Herein, we applied the synchrotron radiation photoelectron spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS) techniques to investigate surface chemistry aspects in a PtNi alloy catalyst under alternating oxidation (O2) and reduction (H2) atmospheres at different temperatures that simulate its behavior as a cathode catalyst in PEMFCs. The experimental results are substantiated by theoretical calculations on model PtNi nanoalloys.We showed that PtNi alloy does not maintain its chemical integrity and undergoes surface reconstruction during the switching between oxidizing and reducing conditions in terms of relative surface nickel enrichment. Along with compositional changes catalyst coarsening was observed by atomic force microscopy (AFM).The revealed behavior of the PtNi alloy provides valuable fundamental insights that help to gain advanced understanding of PtNi alloy catalytic activity in real conditions. Figure 1