Enhancing the intrinsic activity of a benchmarked electrocatalyst such as platinum (Pt) is highly intriguing from fundamental as well as applied perspectives. In this work, hydrogen evolution reaction (HER) activity of Pt electrodes, benchmarked HER catalysts, modified with ultrathin sheets of hexagonal boron nitride (h-BN) is studied in acidic medium (Pt/h-BN), and augmented HER performance, in terms of the overpotential at a 10 mA cm–2 current density (10 mV lower than that of Pt nanoparticles) and a lower Tafel slope (29 ± 1 mV/decade), of the Pt/h-BN system is demonstrated. The effects of h-BN surface modification of bulk Pt as well as Pt nanoparticles are studied, and the origin of such an enhanced HER activity is probed using density functional theory-based calculations. The HER charge transfer resistance of h-BN-modified Pt is found to be drastically reduced, and this enhances the charge transfer kinetics of the Pt/h-BN system because of the synergistic interaction between h-BN and Pt. An enormous reduction in the hydrogen adsorption energy on h-BN monolayers is also found when they are placed over the Pt electrode [−2.51 eV (h-BN) to −0.25 eV (h-BN over Pt)]. Corrosion preventive atomic layers such as h-BN-protected Pt electrodes that perform better than Pt electrodes do open possibilities of benchmarked catalysts by simple modification of a surface via atomic layers.
Nitrogen-doped graphitic carbon materials have been widely used as a catalyst support in the methanol oxidation reaction (MOR). In this study, we report the role of three-dimensionally architectured in-situ N-doped vertically aligned carbon nanofibers (VACNF) as a catalyst support for MOR in acidic and alkaline media. The abundant graphitic edge sites at the sidewall of N-doped VACNF strongly anchor the deposited platinum group metal (PGM) catalysts and induce a partial electron transfer between the PGM catalysts and support. Density Functional Theory (DFT) calculations reveal that the strong metal-support interaction substantially increases the adsorption energy of OH, particularly near the N-doping sites, which helps to compete and remove the adsorbed intermediate species generated during MOR. The PGM catalysts on N-doped VACNF support exhibits CO stripping at lower potentials comparing to the commercial Vulcan carbon support and presents an enhanced electrocatalytic performance and better durability for MOR.
The methanol oxidation reaction (MOR) is the limiting factor in direct methanol fuel cells (DMFC). There is an urgent need to improve the catalytic activity and stability of MOR catalysts. This study reports a highly active PtRu catalyst for MOR based on a hybrid multifunctional catalyst support consisting of a conformal amorphous hydrogenated TiO 2 shell wrapped around the oxygenated N-doped carbon nanotube core, denoted as PtRu/TiO 2 / ONCNT-400. Both the TiO 2 shell and the subsequent PtRu nanoparticles are deposited by a rapid microwave-assisted synthesis processes. The hydrogenated TiO 2 shell is found to exhibit a strong interaction with the deposited PtRu catalyst nanoparticles and effectively prevent them from agglomeration during the postdeposition thermal annealing to form more active crystalline PtRu alloy catalysts. In addition, the defective hydrogenated TiO 2 shell enhances the PtRu catalyst activity by the synergistic effects of partial charge transfer from TiO 2 to PtRu and high oxophilicity, which improves the kinetics of oxidation of poisonous CO intermediate to CO 2 . The mass activity for MOR and long-cycling stability of the PtRu/TiO 2 /ONCNT-400 catalyst surpass the two benchmark commercial PtRu/C catalysts from Johnson Matthey (JM) and Tanaka KiKinzoku (TKK), respectively. The results demonstrate that PtRu/TiO 2 /ONCNT-400 can serve as an efficient catalyst for MOR in DMFC.
We report a scalable method for the preparation of nickel incorporated nitrogen-doped graphene nanoribbon (Ni/NGNRs) through a facile solvothermal process. Significantly, we show that the incorporation of nitrogen functionalities on graphene nanoribbon with tunable nickel content not only catalyzes efficiently the water oxidation reaction but enables to tweak the catalytic reactivity. Thus, Ni/NGNRs composite with higher nickel content exhibits an overpotential of 380 mV with a Tafel slope of 60 mV dec −1 to sustain 10 mA cm −2 under alkaline conditions. Furthermore, only a negligible current density drop is witnessed during the chronoamperometric studies suggesting the robust nature of the electrocatalyst. XPS analysis of the composite before and after polarization studies confirms the formation of nickel oxide on the exposed nickel nanoparticles during the electrochemical reaction but without any major adverse effect on the performance. We attribute the formation of nickel oxide on the exposed nickel nanoparticles as the major reason for the observed enhancement of electrocatalytic performance.
The development of strategies for water‐electrolysis half‐cell‐reaction catalysts without the use of precious metals/metal oxides and the synergistic compilation of catalysts for the full‐cell fabrication are receiving tremendous scientific attention. Here, alkaline water‐electrolysis full cells are developed with novel spongy catalysts for both anode and cathode reactions, such as Co3O4 nitrogen‐doped reduced graphene oxide (Co3O4/NrGO) composite sponge for oxygen evolution reaction (OER) and nickel nitrogen‐doped reduced graphene oxide (NiNrGO) for hydrogen evolution reaction (HER). The performance of the developed OER catalyst, Co3O4/NrGO, is compared with that of the commercial one (IrO2) in alkaline medium with a common benchmark cathode catalyst (Pt) and an augmented full‐cell performance is shown from this novel combination (320 mAcm−2 at an operating voltage of 1.9 V for Co3O4/NrGO, with 199 mA cm−2 for IrO2). A water‐electrolysis full cell is developed without the use of HER catalyst Pt, but rather using a porous spongy catalyst, NiNrGO, having a low operating potential with a high stability (270 mA cm−2 at an operating voltage of 1.9 V with a stability tested for more than 9 h). This work opens up the possibilities of designing lightweight water‐electrolysis cells without the use of commercial benchmark precious‐metal catalysts.
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