Oxygen Reduction Reaction Stability Research Articles

Sr-deficient medium-entropy Sr1-xCo0.5Fe0.2Ti0.1Ta0.1Nb0.1O3-δ cathodes with high Cr tolerance for solid oxide fuel cells

In this work, Sr-deficiency is proposed as an effective strategy to improve the oxygen reduction reaction (ORR) activity and Cr tolerance of medium-entropy Sr1-xCo0.5Fe0.2Ti0.1Ta0.1Nb0.1O3-δ (S1-xCFTTN, x=0–0.15) cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). With proper Sr-deficiency, S0.95CFTTN possesses the highest electrical conductivity and fastest oxygen exchange kinetics within tested samples. The optimized cathode yields outstanding ORR activity with a polarization resistance of 0.024 Ω cm2 at 700 °C, much lower than 0.037 Ω cm2 for SCFTTN cathode. Based on these, an anode-supported cell with S0.95CFTTN cathode exhibits a peak power density of 1153.5 mW cm−2 at 800 °C, much higher than that with SCFTTN cathode. Moreover, the S0.95CFTTN cathode displays dramatically enhanced Cr tolerance ability, which is due to the Sr-deficient diminishes surface Sr segregation and subsequent the formation of SrCrO4. Our results indicate appropriate Sr-deficiency is an effective approach to enhance the ORR activity and stability of SOFC cathodes.

Cobalt-Based Deep Eutectic Solvent Modified Nitrogen-Doped Carbon Catalyst for Boosting Oxygen Reduction Reaction in Zinc–Air Batteries

As an oxygen reduction reaction (ORR) catalyst, nitrogen-doped carbon (NC) is widely used in zinc-air batteries (ZABs). However, NC catalysts exhibit low conductivity and insufficient exposure of active sites. Therefore, a Co-based deep eutectic solvent (DES) was selected to modify NC catalyst (Co-NC) to improve ORR performances. Density functional theory (DFT) calculation shows that the modification of Co-based DES can change the electronic structure of NC and increase metallic active sites, which is beneficial to the desorption of reaction intermediates on Co-NC, further improving ORR performance. Co-NC shows excellent ORR performances and stability. Impressively, ZABs assembled with the Co-NC manifest a high maximum power density of 177.4 mW cm–2, a high specific capacity of 726.12 mA h g–1 and a charge-discharge cycle life of 500 h. This study can provide practical reference for surface modified carbon-based electrocatalyst with DES to improve ORR performances.

Enhanced oxygen reduction catalytic performance of PtNi alloy through modulating metal–support interaction

Tuning metal–support interaction had been regarded as an effective strategy to adjust the electronic structure, catalytic activity and durability of supported metal catalysts. Herein, we design PtNi alloy on nitrogen-doped carbon and SnO2 dual-support and modulate the metal–support interaction. SnO2/PtNi/NC presents strongly coupled SnO2-PtNi-NC interface with lattice overlap of SnO2 (200), Pt (111), Pt (200), and graphitized carbon, along with enhanced electron transfer. SnO2/PtNi/NC has an improved catalytic activity and enhanced stability for oxygen reduction reaction. SnO2/PtNi/NC catalyst had a half-wave potential of 0.886 V versus reversible hydrogen electrode (RHE) in an acidic solution, higher than PtNi/NC (0.785 V vs. RHE) and commercial Pt/C (0.846 V vs. RHE). Furthermore, the current retention of SnO2/PtNi/NC (87.3 %) is also larger than that of commercial Pt/C (56.8 %) and PtNi/NC (19.8 %) after 1000 times start-stops. This study sheds light on the understanding effect of metal–support interaction on the durability of heterogeneous electrocatalysts.

The doping and co-impregnation process for the synthesis of the third metal in Pt3Ni electrocatalysts

Octahedral Pt3Ni on carbon support (Pt3Ni/C) is well-known to be excellent electrocatalysts for the oxygen reduction reaction (ORR) due to its exceptional activity. However, their long-term stability is poor, since the octahedral shape is entirely shattered and Ni is simply leached out during operation. To improve activity and stability, third metals M (i.e., Ga, Ag, Cu, Rh, Co, Fe, and Mo) were added to Pt3Ni electrocatalysts by gas-phase synthesis using two distinct approaches referred to as Co-impregnation (Pt3Ni-M/C) and Metal-doping (M-Pt3Ni/C). The size distributions of octahedron and truncated octahedron were almost identical, with an average particle size of around 8–9 nm for both approaches. The Fe–Pt3Ni/C exhibited the highest pristine ORR activity in terms of both mass activity (1.64 A mgPt−1) and specific activity (65.7 A mgPt−1), which were 2.8 times greater than Pt3Ni/C and 27.3 times more than commercial Pt/C catalyst. For an accelerated durability test (ADT) of 16,000 cycles, the Cu–Pt3Ni/C exhibited the most stable catalysts with an activity retention of 69.9%, followed by Ga-Pt3Ni (61.7%) and Rh–Pt3Ni (52.2%). The Cu–Pt3Ni/C catalyst was 5.8 times more stable than the Pt3Ni/C catalyst. When the same metal was used, it was discovered that the Metal-doping (M-Pt3Ni/C) approach provided superior ORR activity and stability than the Co-impregnation (Pt3Ni-M/C) technique.

The Contact Interface Electronic Coupling of Cobalt and Zirconia Enables Stable and Highly Efficient 4e- Oxygen Reduction ReactionCatalysis.

Cobalt (Co) is an efficient oxygen reduction reaction (ORR) catalyst but suffers from issues of easy deactivation and instability. Here, it shows that ZrO2 can stabilize Co through interface electron coupling and enables highly efficient 4e- ORR catalysis. Porous carbon nanofibers loaded with dispersed Co-nanodots (≈10nm, 9.63wt%) and ZrO2 nanoparticles are synthesized as the catalyst. The electron transfer from the metallic Co to ZrO2 causes interface-oriented electron enrichment that promotes the activation and conversion of O2, improving the efficiency of 4e- transfer. Moreover, the simulation results show that ZrO2 acts like an electron reservoir to store electrons from Co and slowly release them to the interface, solving the easy deactivation problem of Co. The catalyst exhibits a high half-wave potential (E1/2) of 0.84V, which only decreases by 3.6mV after 10000 cycles, showing great stability. Particularly, the enhanced spin polarization of Co in a magnetic field reinforces the interface electron coupling that increases the E1/2 to 0.864V and decreases the energy barrier of ORR from 0.81 to 0.63eV, confirming that the proposed strategy is effective for constructing efficient and stable ORR catalysts.

Improvement of oxygen reduction activity and stability on a perovskite oxide surface by electrochemical potential

The instability of the surface chemistry in transition metal oxide perovskites is the main factor hindering the long-term durability of oxygen electrodes in solid oxide electrochemical cells. The instability of surface chemistry is mainly due to the segregation of A-site dopants from the lattice to the surface. Here we report that cathodic potential can remarkably improve the stability in oxygen reduction reaction and electrochemical activity, by decomposing the near-surface region of the perovskite phase in a porous electrode made of La1-xSrxCo1-xFexO3 mixed with Sm0.2Ce0.8O1.9. Our approach combines X-ray photoelectron spectroscopy and secondary ion mass spectrometry for surface and sub-surface analysis. Formation of Ruddlesden-Popper phase is accompanied by suppression of the A-site dopant segregation, and exsolution of catalytically active Co particles onto the surface. These findings reveal the chemical and structural elements that maintain an active surface for oxygen reduction, and the cathodic potential is one way to generate these desirable chemistries.

ORR activity and stability of carbon supported Pt3Y thin films in PEMFCs

In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 VRHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.

Precise synthetic control of exclusive ligand effect boosts oxygen reduction catalysis

Ligand effect, induced by charge transfer between catalytic surface and substrate in core/shell structure, was widely proved to benefit Pt-catalyzed oxygen reduction reaction by tuning the position of d-band center of Pt theoretically. However, ligand effect is always convoluted by strain effect in real core/shell nanostructure; therefore, it remains experimentally unknown whether and how much the ligand effect solely contributes electrocatalytic activity improvements. Herein, we report precise synthesis of a kind of Pd3Ru1/Pt core/shell nanoplates with exclusive ligand effect for oxygen reduction reaction. Layer-by-layer growth of Pt overlayers onto Pd3Ru1 nanoplates can guarantee no lattice mismatch between core and shell because the well-designed Pd3Ru1 has the same lattice parameters as Pt. Electron transfer, due to the exclusive ligand effect, from Pd3Ru1 to Pt leads to a downshift of d-band center of Pt. The optimal Pd3Ru1/Pt1-2L nanoplates achieve excellent activity and stability for oxygen reduction reaction in alkaline/acid electrolyte.

Electronic structure modification of FeWO4 through F doping for enhanced oxygen reduction performance in zinc–air batteries

Exploring efficient and stable oxygen reduction reaction (ORR) catalysts for zinc-air batteries (ZABs) holds tremendously significant. Tungsten-based materials have attracted the attention of researchers thanks to abundant resources and excellent stability. Nevertheless, due to the strong adsorption energy for O-containing intermediates, *O and *OH are difficult to desorb from tungsten-based materials during ORR. Here, an F-doping strategy was employed to construct F-doped FeWO4 species composited on a multi-dimensional N-doped carbon (F–FeWO4/NC) as the ORR catalyst for ZABs. The incorporation of F atoms into the main lattice of FeWO4 enhanced the polarity of chemical bonds in FeWO4 through hydrogen bond interactions between H2O molecules and F atoms, further enhancing the polarity and hydrophilicity of F–FeWO4/NC. These changes favored the adsorption and desorption of intermediates as well as the diffusion of electrolyte, and ultimately reduced the ORR overpotential. Therefore, the F–FeWO4/NC catalyst demonstrated excellent ORR activity (E1/2 = 0.85 V vs. RHE). Furthermore, the ZAB with F–FeWO4/NC yielded satisfactory a specific capacity of 800.2 mAh g−1, a peak power density of 173.5 mW cm−2, and charge-discharge cycling stability (over 170 h at 5 mA cm−2). This study is beneficial to improve the ORR intrinsic activity of cheap tungsten-based materials and provides theoretical guidance for their practical application in ZABs.

Integrating PtCo nanoparticles on N, S doped pore carbon nanosheets as high-performance bifunctional catalysts for oxygen reduction and hydrogen evolution reactions

The development of low-Pt bifunctional electrocatalysts with excellent performance for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for the advancement of the hydrogen economy. Here, we have integrated low-loading Pt and Co metals into N, S doped porous carbon nanosheets to obtain composite catalysts encapsulating PtCo alloy nanoparticles (PtCo2@Co9S8/N-CNS and PtCo2@N-CNS). The acquired PtCo nanoparticles, with dimensions of about 2.5 nm, are uniformly distributed and firmly anchored in N, S doped carbon nanosheets with large specific surface areas and rich pore structure, forming multiple active centers and effectively preventing the aggregation of metal nanoparticles. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS display high ORR catalytic mass activity of 1.65 A mgPt-1 and 1.01 A mgPt-1 in 0.1 M HClO4. The PtCo2@N-CNS catalyst exhibits excellent HER performance in 0.5 M H2SO4, with a mass activity (at 50 mV) 4.3 times higher than that of Pt/C. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS also exhibit stronger ORR and HER stability than Pt/C after accelerated durability tests. The superior catalytic activity performance of catalysts can be attributed to the synergistic effect of multiple active centers of PtCo, Co9S8 and Co-N in the catalysts. The confinement of PtCo nanoparticles by Co metal and N, S doped porous nanosheets derived from graphitic carbon nitride (g-C3N4) as the template, which can effectively prevent the corrosion and migration of the catalysts under acidic conditions, enhances the catalytic stability of the materials. This study provides a new perspective for the development of economical and efficient bifunctional low-Pt catalysts.

Surface curvature effect on single-atom sites for the oxygen reduction reaction: A model of mesoporous MOF-derived carbon

Iron-based single-atom catalysts (Fe-SACs) containing Fe–N4 active sites have shown immense potential in the oxygen reduction reaction (ORR). However, the limited ability to adsorb O2 and catalyze subsequent O–O bond breaking on Fe–N4 sites has hindered their full potential, especially in acidic electrolytes. Here, we present an approach by utilizing a tunable curved surface to enhance the activity of Fe–N4 active sites, with theoretical calculations, demonstrating that Fe–N4 sites anchored on low–curvature surfaces (lc-Fe-N4) is favirable for ORR. Experimental results show that the catalyst exhibits excellent catalytic activity and stability for ORR in acidic electrolytes, with a half-wave potential of 0.82 V vs. RHE, approaching that of commercial Pt/C. This work develops an approach for promoting the catalytic activity by anchoring atomically dispersed Fe–N4 sites, unlocking their potential for extended use in electrocatalytic and energy storage applications.

Effect of Ni loading onto Pt (Pt‐Ni/C) electrocatalysts for PEM fuel cell: A study of ORR activity, stability, and temperature effect

AbstractPt is a noble metal when alloyed with transition metals like Ni onto the carbon support, minimizes the cost and increases the oxygen reduction reaction (ORR) activity and stability of Pt‐Ni/C electrocatalyst in a low‐temperature proton exchange membrane (LTPEM) fuel cell. A simple sonochemical‐based synthesis of Pt‐Ni/C bimetallic nanoparticles is carried out through varying amounts of Ni and Pt precursors. The various combinations of Pt and Ni metal (50:50, 75:25, and 83:17) nanoparticles were uniformly distributed on a carbon support. The shifting of 2θ values to higher levels in XRD patterns confirmed the alloy formation between Pt and Ni. The carbon (60 wt. %) supported Pt and Ni (40 wt. %) electrocatalyst ink is coated on a carbon paper which acts as a gas diffusion layer (GDL). The electrocatalytic performance of Pt‐Ni/C was evaluated in the PEM fuel cell using an electrochemical test station. The best performance was observed with the Pt: Ni (83:17) coated electrocatalyst, which delivered 0.162 W/cm2 power at 0.45 V. Also, the PEM fuel cell performance was enhanced by increasing the single cell's operating temperature.

Nickel Phosphonate MOF Derived N-Doped Carbon-Coated Phosphorus-Vacancies-Rich Ni2 P Particles as Efficient Bifunctional Oxygen Electrocatalyst.

The design of non-noble metal bifunctional electrocatalysts with outstanding performance and remarkable stability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the most essential issues to the realization of rechargeable zinc-air battery, and transition metal phosphides (TMPs) have emerged as robust candidates for oxygen electrocatalysts. Herein, N-doped carbon-coated phosphorus-vacancies-rich Ni2 P particles (Vp -Ni2 P@NC) is proposed via simple carbonization and following Ar plasma treatment from a single nickel phosphonate metal-organic framework (MOF) without extra phosphine and nitrogen sources. The facile and rapid plasma treatment can achieve phosphorus vacancies which could modulate the electronic structure to enhance the inherent active and electrical conductivity. Meanwhile, the pyridine-N and graphitized-N produced during calcination also could provide more active sites and increase the electrical conductivity. The resultant Vp -Ni2 P@NC catalyst shows excellent bifunctional electrocatalytic activity (OER/ORR) based on synergistic effect of introducing P vacancies into Ni2 P and N-doped carbon. Vp -Ni2 P@NC catalyst shows more advantageous ΔE value (0.70 V) compared to Pt/C+RuO2 (0.73 V) and most reported catalysts. Additionally, the zinc-air bbatterie (ZAB) employing Vp -Ni2 P@NC as air cathode shows excellent performance. The maximum power density of 203.48 mW cm-2 , the cycling stability of more than 150 h at 10 mA cm-2 .

Cerium oxide boosted CoFe-N codoped carbon nanotubes with abundant oxygen-vacancies toward efficient oxygen reduction and methanol oxidation reaction

In this study, we designed a novel strategy that utilizes N-doped carbon nanotubes as the chemical bond supporter to stabilize ultrafine CoFe alloy and introduces secondary CeO2 active sites into the hybrid, resulting in the formation of CeO2/CoFe-NCNTs heterostructures with exceptional bifunctional electrocatalytic capabilities. To be specific, solution dispersion and high-temperature calcination methods were employed to create the CoFe-NCNTs active sites through the introduction of ethylenediamine into the network interstitials of Co-EDTA and Fe-EDTA. The CeO2/CoFe-NCNTs hybrid not only promotes oxygen absorption and conversion of intermediates, but also accelerates charge transfer capability, thus enhancing oxygen reduction reaction (ORR) performance, while simultaneously inducing boosted the methanol oxidation reaction (MOR) activity. Moreover, the well-dispersed CoFe nanoparticles within the hybrid hold significant potential for establishing metal-nitrogen bonds with the N-doped carbon nanotube network, resulting in efficient catalytic behavior driven by synergistic effects with CeO2 nanoparticles, which contributes to reactant activation. As expected, the resultant CeO2/CoFe-NCNTs-2 exhibits remarkable electrocatalytic performance, with a current density of 281.40 mA cm−2 at a scan rate of 200 mV s−1 and a low Tafel slope (71.3 mV dec−1) for MOR, as well as achieving excellent half-wave potential and onset potential values of 0.834 and 0.90 V (vs. RHE) for ORR. Additionally, it exhibits durable cycle stability for both MOR and ORR, retaining 92.8% and 96.4% of its initial current density during the I-t test, respectively. This work establishes a highly efficient bifunctional earth-abundant electrocatalysts for both anode and cathode reactions in methanol fuel cells.

Nitrogen-doped carbon/graphitic CQDs composites with 98.8% microporosity as a highly stable electrocatalyst for oxygen reduction

Designing micropore-rich carbon materials with large specific surface area (SSA) as a carbon-based oxygen reduction reaction (ORR) electrocatalyst is still frontier but remains challenging in catalysis of zinc-air batteries. Here we propose a new strategy for synthesis of nitrogen atoms co-doped carbon sheets and carbon quantum dots (N-C@CQDs) with an SSA of 1485.3 m2 g−1 and 98.8 % micro-porosity from α-cellulose via using a complex salt (ZnCl2-NH4Cl) with low eutectic point (179 °C) as a pore regulator and K2FeO4 as a graphitization catalyst, which can serve as an active and stable carbon-based ORR electrocatalyst. The role of K2FeO4 not only promotes graphitization but also oxidizes the large-sized graphitic carbon particles into a huge amount of uniformly distributed CQDs. This catalyst has exhibited a comparable ORR activity and superior stability to the Pt/C, but a Zn-air battery assembled with the former has delivered a higher peak power density (214 mW cm−2) and a larger gravimetric energy density (ED) of (959 Wh kgZn-1), especially in which it also displays an outstanding catalytic durability with 98.7 % ED retention during a ∼110 h continuous discharge. This work provides a new pathway for design of high-performance carbon-based ORR catalysts in various energy devices.

A 3D Covalent Organic Framework with In-situ Formed Pd Nanoparticles for Efficient Electrochemical Oxygen Reduction.

Non-platinum noble metals are highly desirable for the development of highly active, stable oxygen reduction reaction (ORR) electrocatalysts for fuel cells and metal-air batteries. However, how to improve the utilization of non-platinum noble metals is an urgent issue. Herein, a highly efficient catalyst for ORR was prepared through homogeneous loading of Pd precursors by a domain-limited method in a three-dimensional covalent organic framework (COF) followed by pyrolysis. The morphology of the Pd nanoparticles (Pd NPs) was well maintained after carbonization, which was attributed to the rigid structure of the 3D COF. Thanks to the uniform distribution of Pd NPs in the carbon, the catalyst exhibited a remarkable half-wave potential of 0.906 V and a Tafel slope of 70 mV dec-1 in 0.1 M KOH, surpassing the commercial Pt/C catalyst (0.863 V and 75 mV dec-1 ). Furthermore, a maximum power density of 144.0 mW cm-2 was achieved at 252 mA cm-2 , which was significantly higher than the control battery (105.1 mW cm-2 ). This work not only provides a simple strategy for in-situ preparation of highly dispersible metal catalysts in COFs, but also offers new insights into the ORR electrocatalysis.

Improvement of the electrocatalytic performance of silicon carbide for oxygen reduction reaction induced by nitrogen doping

Replacing the precious metal catalysts with low-cost, efficient and stable catalysts for oxygen reduction reaction (ORR) is necessary to solve the challenge of sluggish reaction kinetics. Commercial SiC and aniline were used as a precursor and nitrogen source to prepare a series of nitrogen-doped SiC electrocatalysts (N-SiC) by a facile pyrolysis method at different temperature (800–1100 °C) under nitrogen atmosphere. Among four N-SiC samples, N-SiC-1000 possesses the highest surface area, uniform nanorod morphology, highest nitrogen content, and positively shifted binding energy. Based on these characteristics, the N-SiC-1000 catalyst demonstrates the best ORR catalytic activity manifested by relatively positive onset potential of 1.01 V, half-wave potential (0.87 V) and highest current density (5.38 mA cm−2 at 0.4 V), which is comparable to that of Pt/C, and has significantly better stability and outstanding methanol tolerance than that of Pt/C. The number of electrons transferred of N-SiC-1000 for ORR process is ∼3.97, indicating a 4-electron reaction pathway. These results show that N-SiC-1000 is a low-cost, efficient and stable ORR catalyst and can be used as a substitute for precious metal catalyst in fuel cells application.

Modulating metal-support interaction between Pt3Ni and unsaturated WOx to selectively regulate the ORR performance

Tuning strong metal-support interaction between Pt-based alloys and metal oxides is an effective strategy for modulating the performance of oxygen reduction reaction (ORR). Herein, Pt3Ni alloy anchored on WOx with different content of oxygen vacancies is synthesized, and the effect of unsaturated WOx on ORR activity/stability is revealed. Electrochemical results indicate that ORR activity is positively correlated with oxygen vacancy concentration, while durability presents the opposite trend. Density functional theory (DFT) calculation results suggest that controlling the content of oxygen vacancies can usefully adjust the charge redistribution between Pt3Ni and WOx, which can optimize the adsorption/activation of reactants, thus obtaining good ORR activity. This study uncovers the effect of unsaturated WOx on ORR performance for Pt-based alloys and provides a promising strategy to design efficient and stable ORR catalysts.

Mesoporous and dual-shelled hollow CeO2@CoNC nanospheres as efficient and stable oxygen reduction reaction electrocatalysts

The electrocatalytic oxygen reduction reaction (ORR) is the key bottleneck of fuel cells and rechargeable metal-air batteries, and recently, metalnitrogen complex carbon (MNC) demonstrates great potential in these fields. However, the complex and easily degraded MNC structure often results in inferior activity and poor durability in electrolysis. Herein, we fabricate a catalyst of h-CeO2@CoNC through the extended Stöber method and subsequent pyrolysis, involving the hollow CeO2 as the core and CoNC as the shell. The h-CeO2@CoNC catalyst exhibits notable ORR catalytic performances in 0.1 M KOH with a half-wave potential of 0.82 V and excellent durability, attributed to the synergistic interaction between CeO2 and CoNC matrix. Specifically, the inner layer of CeO2 is principally responsible for enhancing the chemical stability and the outer one of CoNC matrix is beneficial to boosting the ORR catalytic activity. This work provides an efficient preparation approach and further insight of rational design of the unique MNC catalysts for energy storage.

Manipulating Pt-skin of porous network Pt-Cu alloy nanospheres toward efficient oxygen reduction

Designing Pt-skin on the catalyst surface is critical to developing efficient and stable electrocatalysts toward oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. In this paper, an acidic reductant is proposed to synchronously manipulate in-situ growth of Pt-skin on the surface of alloyed Pt-Cu nanospheres (PtCuNSs) by a facile one-pot synthesis in an aqueous solution. Ascorbic acid can create a Pt-skin of three atomic layers to make the typical PtCu-alloy@Pt-skin core/shell nanostructure rather than the uniform alloys generated by using alkaline reductants. Surfactant as soft-template can make the alloyed PtCuNSs with a three-dimensional porous network structure. Multiple characterizations of XRD, XPS and XAFS are used to confirm Pt-alloying with Cu and formation of core/shell structure of such a catalyst. This PtCuNSs/C exhibits a half-wave potential of 0.913 V (vs. RHE), with mass activity and specific activity about 3.5 and 6.4 times higher than those of Pt/C, respectively. Fuel cell tests verify the excellent activity of PtCuNSs/C catalyst with a maximum power density of about 1.2 W cm−2. Moreover, this catalyst shows excellent stability, achieving a long-term operation of 40,000 cycles. Furthermore, theoretical calculations reveal the enhancement effect of characteristic PtCu-alloy@Pt-skin nanostructure on both catalytic ORR activity and stability.