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The oxygen reduction reaction (ORR) that occurs on the outermost layer of electrocatalysts is significantly affected by the composition and structure of the electrocatalysts. During the preparation of PtM alloy electrocatalysts, high-temperature annealing in an inert or reducing atmosphere could promote the segregation of M toward the core, forming a highly active Pt-skin structure. However, under fuel cell operating conditions, the adsorption of oxygen-containing groups could stimulate the easily dissolved M to segregate to the surface, reducing the activity and stability of the electrocatalysts. In this work, we conducted segregation energy calculation of PtM (M = Cu, Pd, Au) electrocatalysts under specific adsorption (SA), aqueous solution (AS) and an external electric field (EEF) with a density functional theory method. It was found that different factors have different effects on the segregation energy: ΔΔESA ≫; ΔΔEEEF > ΔΔEAS. The coupling effects have also been considered and compared: ΔΔESA+EEF > ΔΔESA+AS > ΔΔEEEF+AS. When including all three factors, the change of segregation energy could reach 1.63 eV. Therefore, operating conditions have a noteworthy influence on the segregation behavior of PtM ORR electrocatalysts, which should be considered in the further design of PtM ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

The strain effect on oxygen reduction reaction (ORR) activity and stability of FeNC electrocatalysts has been studied using density functional theory in this work. Based on the reaction free energy results, the rate-determining step (RDS) of ORR on FeNC is *OH → H2O, and the reaction proceeds with the pathway O2 → *OOH → *O → *OH → H2O on the Fe site. Tensile stress is favorable to enhance the ORR activity, and the highest ORR activity is obtained on the 6%-FeNC electrocatalyst. On the other hand, when the whole oxygen reduction process needs synergy between Fe and adjacent C atoms and proceeds with the pathway O2 → *OOH → *TS → *O & #OH → *O → *OH → H2O, the applied stress will decrease the ORR activity of the FeNC electrocatalyst. We further constructed a Cu@FeNC core–shell model to simulate strained FeNC. However, the adsorption energy of ORR intermediates on Cu@FeNC (1.9%-FeNC) is much weaker than on the corresponding 2%-FeNC, mainly due to the coordination between the Cu substrate and Fe atom. In addition, the formation energy and binding energy indicate that neither tensile nor compressive stress is conducive to the stability of the FeNC electrocatalyst. In summary, tensile stress could enhance the ORR activity of FeNC electrocatalysts when ORR occurs on the Fe atom only. What's more, we should pay more attention to the influence of interface interaction if utilizing a M@FeNC model to achieve strained FeNC. [ABSTRACT FROM AUTHOR]

Direct methanol fuel cells (DMFCs) have drawn extensive interest for the past two decades both in scientific research and industrial engineering circles for their advantages of high energy density, environmental friendliness, and easy fuel handling. However, their excessively high costs, especially derived from the massive use of precious metal catalysts in both their anodes and cathodes, hamper the commercialization of this technology to the general public. Though the production of inexpensive catalysts of methanol oxidation remains challenging, non-precious-metal-based catalysts of the oxygen reduction reaction have seen considerable technical progress, yielding remarkable performance levels in hydrogen-fueled polymer electrolyte membrane fuel cells (PEMFCs). Due to the particularities of the electrochemical reactions and mass transport for methanol fuel in DMFC electrodes, highly active non-precious metal catalysts have not yielded sufficiently satisfactory single-cell performances for practical applications. In the current work, rather than exploring the cathodic designs with advanced electrode materials and structures, we estimated the mass transport of methanol and its effects on cathode performance, and then redesigned the anode architecture with ultrathin gas diffusion layers based on carbon nanotube composite materials. By using such an alternative strategy focused on anodic engineering to accelerate methanol transport combined with the use of a methanol-inert cathode, an ultrahigh cell performance, comparable to those of Pt–C-containing cathodes, was achieved even at a low methanol concentration. The peak power density obtained was 141 mW cm−2, a value among the highest obtained from DMFCs with non-precious-metal catalyst cathodes to the best of our knowledge. A wider avenue of DMFC technologies for practical applications might be opened with further development of this work. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) plays a critical role in efficient conversion and storage of renewable energy sources, whereas the active sites for the most representative electrocatalysts, Ni–Fe compounds, remain under debate. In this work, we have developed polymeric carbon nitride (PCN) with atomically dispersed N-coordinated Ni–Fe sites to investigate the OER process. The Ni–Fe dual sites consist of adjacent Ni and Fe atoms coordinated with N atoms in the PCN matrix. NiFe-codoped PCN exhibits higher electrocatalytic activity than monometal-doped catalysts, showing a lower overpotential (310 mV at 10 mA cm−2) and smaller Tafel slope (38 mV dec−1) in 1 M KOH, indicating that Ni–Fe dual-metal sites significantly favor the OER process. According to density functional theory calculations based on the oxidized-NiFe@PCN model, it was found that adjacent Ni and Fe atoms co-participate in the OER process for NiFe-codoped PCN, leading to a much lower energy barrier (0.10 or 0.22 eV for U = 1.58 V), while the effect of electronic modification of the single metal active sites by the other component (Ni sites by Fe sites or vice versa) contributes less to activity enhancement, thus leading to a rational explanation on the synergistic effect of the NiFe-based OER catalysts. [ABSTRACT FROM AUTHOR]

The fabrication of a novel electrode architecture with multi-scale orderliness is an effective strategy to enhance Pt utilization and decrease the mass transport polarization loss of proton exchange membrane fuel cells (PEMFCs). Here we report a hierarchically well-defined electrode with Pt nanowhiskers on aligned nanowires by a magnetron sputtering method. With the crystallographically preferential growth of Pt (111) facets, in association with the electron modification effects of PANI on Pt nanowhiskers, the electrode achieves outstanding electrochemical activity towards the oxygen reduction reaction (ORR) with a 2.19-fold enhancement of the specific activity and a similar mass specific activity at 0.9 V (vs. the RHE), compared to the state-of-the-art Pt–C electrode. The PEMFC fabricated with the Pt–PANI-GDL electrode shows excellent performance with a peak power density of 542 mW cm−2, and a cathode mass specific power density of 5.7 W mgPt−1, which is 39% greater than that of PEMFCs equipped with a Pt–C electrode for enhanced electrochemical activity and mass transport. [ABSTRACT FROM AUTHOR]

Carbon black nanoparticles localized in-between liposomal bi-layers provide a unique reaction environment that permits one-step synthesis of carbon-supported foam-like platinum (Pt foam/C) in aqueous solution under ambient conditions. The obtained Pt foam/C was readily purified by simple washing with water and chloroform at room temperature. Unlike commercial Pt/C composed of quasi-spherical nanoparticles, Pt foam/C consists of convoluted dendritic nanosheets. Interestingly, Pt foam/C demonstrated both improved durability and activity toward oxygen reduction reaction (ORR). The improved durability is because of the formation of metastable nano-holes among dendritic branches of Pt foam/C under ripening, preserving the surface area. The activity enhancement of Pt foam/C can be attributed to predominantly exposed Pt {1,1,0} planes that possess the highest ORR activity among all low-indexed Pt crystalline planes. Nano-scale Pt primarily enclosed by {1,1,0} planes has not been reported previously. [ABSTRACT FROM AUTHOR]

Non-noble metal (NNM) electrocatalysts with performances comparable with or superior to Pt are highly desirable for fuel cells and metal-air batteries, but remain rare. Herein, we report a new NNM electrocatalyst derived from reduced graphene oxide (rGO), dual nitrogen-containing ligands, and iron and cobalt salts. Remarkably, the onset potential and half-wave potential (E1/2) of the obtained electrocatalyst shifts 5 and −23 mV, respectively, relative to commercial Pt/C at a standard loading of 20 μgpt cm−2 toward an oxygen reduction reaction (ORR) in alkaline solutions. Additionally, the electrocatalyst is much better than the Pt/C in terms of durability and tolerance to methanol. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) that occurs on the outermost layer of electrocatalysts is significantly affected by the composition and structure of the electrocatalysts. During the preparation of PtM alloy electrocatalysts, high-temperature annealing in an inert or reducing atmosphere could promote the segregation of M toward the core, forming a highly active Pt-skin structure. However, under fuel cell operating conditions, the adsorption of oxygen-containing groups could stimulate the easily dissolved M to segregate to the surface, reducing the activity and stability of the electrocatalysts. In this work, we conducted segregation energy calculation of PtM (M = Cu, Pd, Au) electrocatalysts under specific adsorption (SA), aqueous solution (AS) and an external electric field (EEF) with a density functional theory method. It was found that different factors have different effects on the segregation energy: ΔΔESA ≫ ΔΔEEEF > ΔΔEAS. The coupling effects have also been considered and compared: ΔΔESA+EEF > ΔΔESA+AS > ΔΔEEEF+AS. When including all three factors, the change of segregation energy could reach 1.63 eV. Therefore, operating conditions have a noteworthy influence on the segregation behavior of PtM ORR electrocatalysts, which should be considered in the further design of PtM ORR electrocatalysts.

Monomorphic Pt octapod and tripod nanocrystals have been successfully synthesized by an iron nitrate modified polyol process, in which iron nitrate has been proven to be vitally important for slowing down the reduction rate of Pt precursors., (This journal is © The Royal Society of Chemistry 2011)

A novel carbon-supported palladium-rich Pd3Pt1/C catalyst prepared by a modified polyol process showed a better cell performance than Pt/C in direct methanol fuel cells, which may be attributed to palladium's inactivity to methanol electro-oxidation while exhibiting good performance to oxygen reduction reaction.