PtNi alloy nanoparticles grown in situ on nitrogen doped carbon for the efficient oxygen reduction reaction

Currently, Pt based materials are still the most efficient oxygen reduction reaction (ORR) catalysts. However, their poor stability obstructs the commercial viability of fuel cells. To lower the reaction potential barrier and enhance the stability, we constructed alloy PtNi nanoparticles (NPs) with a Pt-rich surface supported on nitrogen-doped carbon (NC) via a simple one-step solvothermal method using easily accessible reagents. The synthesized PtNi/NC exhibits enhanced mass activity (MA), specific activity (SA), and positive onset potential compared with commercial Pt/C catalysts. Meanwhile, the half-wave potential shifted negatively to only 18 mV after 5000 cycles for PtNi/NC, indicating excellent stability. The enhanced ORR performance can be ascribed to the introduction of Ni into Pt optimizing the adsorption energy of Pt towards oxygen by adjusting the d band center of the Pt atom and stronger interaction between the metal NPs and support. Our work provides a potential synthesis strategy for developing a Pt-based catalyst with a low Pt loading and high ORR performance.

One-pot production of a sea urchin-like alloy electrocatalyst for the oxygen electro-reduction reaction

Designing a cost-effective catalyst with high performance towards the oxygen electro-oxidation reaction (ORR) is of great interest for the development of green energy storage and conversion technologies. We report herein a facile self-assembly strategy in a mild reducing environment to realize an urchin-like NiPt bimetallic alloy with the domination of the (111) facets as an efficient ORR electrocatalyst. In the rotating-disk electrode test, the as-obtained NiPt nanourchins (NUCs)/C catalyst demonstrates an increase in both onset potential (0.96 V_RHE) and half-wave potential (0.92 V_RHE) and a direct four-electron ORR pathway with enhanced reaction kinetics. Additionally, the as-made NiPt NUCs/C electrocatalyst also shows impressive ORR catalytic stability compared to a commercial Pt NPs/C catalyst after an accelerated durability test with 15.29% degradation in mass activity, which is 3.04-times lower than 46.48% of the Pt NPs/C catalyst. The great ORR performance of the as-made catalyst is due to its unique urchin-like morphology with the dominant (111) facets and the synergistic and electronic effects of alloying Ni and Pt. This study not only provides a robust ORR electrocatalyst, but also opens a facile but effective route for fabricating 3D Pt-based binary and ternary alloy catalysts.

Gram-Scale Synthesis of Carbon-Supported Sub-5 nm PtNi Nanocrystals for Efficient Oxygen Reduction

The preparation of a high performance and durability with low-platinum (Pt) loading oxygen reduction catalysts remains a challenge for the practical application of fuel cells. Alloying Pt with a transition metal can greatly improve the activity and durability for oxygen reduction reaction (ORR). In this work, we present a one-pot wet-chemical strategy to controllably synthesize carbon supported sub-5 nm PtNi nanocrystals with a ~3% Pt loading. The as-prepared PtNi/C-200 catalyst with a Pt/Ni atomic ratio of 2:3 shows a high oxygen reduction activity of 0.66 A mgpt−1 and outstanding durability over 10,000 potential cycles in 0.1 M KOH in a half-cell condition. The PtNi/C-200 catalyst exhibits the highest ORR activity, with an onset potential (Eonset) of 0.98 V and a half-wave potential (E1/2) of 0.84 V. The mass activity and specific activity are 3.89 times and 9.16 times those of 5% commercial Pt/C. More importantly, this strategy can be applied to the gram-scale synthesis of high-efficiency electrocatalysts. As a result, this effective synthesis strategy has a significant meaning in practical applications of full cells.

Cylindrical C96 Fullertubes: A Highly Active Metal-Free O2 -Reduction Electrocatalyst

A new isolation protocol was recently reported for highly purified metallic Fullertubes D_5h -C₉₀ , D_3d -C₉₆ , and D_5d -C_100, which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C₆₀ , C₇₀ (spheroidal fullerenes), and C₉₀ , C₉₆ , and C₁₀₀ (tubular fullerenes) using a combination of experimental and theoretical approaches. C₉₆ (a metal-free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state-of-the-art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm^-2 using C₉₆ as a modified cathode in a proton-exchange membrane fuel cell, comparable to other recently reported efficient metal-free catalysts. Combined band structure (experimentally calculated) and free-energy (DFT) investigations show that both favorable energy-level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C₉₆ .

Gram-Scale Synthesis of Well-Dispersed Shape-Controlled Pt-Ni/C as High-Performance Catalysts for the Oxygen Reduction Reaction

To further promote the development and industrialization of the fuel cell, it is urgent to exploit the high-performance catalysts prepared by simple and effective methods. Here, an effective and simple one-pot synthesis of well-dispersed Pt-Ni/C catalysts is reported. The shape-controlled 10 nm-sized Pt-Ni catalysts are successfully synthesized. Among them, the Pt-Ni/C-8h with a concave structure shows the best performance in the RDE test. Its concave structure makes it possess plentiful active sites and a higher platinum utilization, which help the catalytic performance. The mass activity (MA) and specific activity (SA) are nearly 13.8 and 12.5 times higher than those of commercial Pt/C catalysts (JM). After the accelerated durability test, the half-wave potential of Pt-Ni/C concave octahedron catalyst only shifted 9 mV and the mass activity could maintain 72.5%. In single cell tests, the MEA prepared by Pt-Ni/C-12h exhibits the best performance, which is 1.2 times that sprayed by Pt/C. It indicates that these nanoparticles can be promising catalysts to be applied to proton exchange membrane fuel cells (PEMFC).

Insight on the Interaction of Methanol-Selective Oxidation Intermediates with Au- or/and Pd-Containing Monometallic and Bimetallic Core@Shell Catalysts

Using density functional theory (DFT), the interaction of crucial molecules involved in the selective partial oxidation of methanol to methyl formate (MF) with monometallic Au and Pd and bimetallic Au/Pd and Pd/Au core@shell catalysts is systematically investigated. The core@shell structures modeled in this study consist of Au(111) and Pd(111) cores covered by a monolayer of Pd and Au, respectively. Our results indicate that the adsorption strength of the molecules examined as a function of catalytic surface decreases in the order of Au/Pd(111) > Pd(111) > Au(111) > Pd/Au(111) and correlates well with the d-band center model. The preadsorption of oxygen is found to have a positive impact on the selective partial oxidation reaction because of the stabilization of CH3OH and HCHO on the catalyst surface and the simultaneous intensification of MF desorption. On the basis of a dynamical matrix approach combined with statistical thermodynamics, we propose a simple route for evaluating the Gibbs free energy of adsorption as a function of temperature. This method allows us to anticipate the relative temperature stability of molecules involved in the selective partial oxidation of methanol to MF in terms of catalytic surface.

Effects of oxygen coverage, catalyst size, and core composition on Pt-alloy core–shell nanoparticles for oxygen reduction reaction

This study focuses on the analysis of Pt-based alloy nanoparticles as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC) technology.