In this work, the effects of the addition of transition metals (Mn, Fe, Co, Ni, Cu) on the structure and performance of the doped carbon catalysts M-PANI/C-Mela are investigated. The results show ...that the doping of various transition metals affected structures and performances of the catalysts significantly. Doping with Fe and Mn leads to a catalyst with a graphene-like structure, and doping with Co, Ni, and Cu leads to a disordered or nanosheet structure. The doping of transition metals can enhance the performance of the catalysts, and their ORR activity follows the order of Fe > Co > Cu > Mn > Ni, which is consistent with the order of their active N contents. We suggest that the various performance enhancements of the transition metals may be the result of the joint effect of the following three aspects: the N content/active N content, metal residue, and the surface area and pore structure, but not the effect of any single factor.
Well defined nitrogen-doped graphene (NG) is prepared by a transfer doping approach, in which the graphene oxide (GO) is deoxidized and nitrogen doped by the vaporized polyaniline, and the GO is ...prepared by a thermal expansion method from graphite oxide. The content of doped nitrogen in the doped graphene is high up to 6.25 at% by the results of elements analysis, and oxygen content is lowered to 5.17 at%. As a non-precious metal cathode electrocatalyst, the NG catalyst exhibits excellent activity toward the oxygen reduction reaction, as well as excellent tolerance toward methanol. In 0.1 M KOH solution, its onset potential, half-wave potential and limiting current density for the oxygen reduction reaction reach 0.98 V (vs. RHE), 0.87 V (vs. RHE) and 5.38 mA cm super(-2), respectively, which are comparable to those of commercial 20 wt% Pt/C catalyst. The well defined graphene structure of the catalyst is revealed clearly by HRTEM and Raman spectra. It is suggested that the nitrogen-doping and large surface area of the NG sheets give the main contribution to the high ORR catalytic activity.
Uniform nitrogen and sulfur co-doped carbon nanospheres with an average diameter of approximately 200nm were prepared using sulfur and polyacrylonitrile as precursors. The materials were ...characterized using scanning electron microscopy, transmission electron microscopy, elemental analysis, and X-ray photoelectron spectroscopy. The characterization results suggest the as-prepared materials had uniform, porous, nanospherical morphologies and high surface areas. For the typical sample containing 9.5% sulfur, the surface area is up to 653m2g−1. The catalysts exhibited enhanced catalytic activity, outstanding long-term stability, and excellent methanol tolerance in an alkaline medium. Significantly, the sulfur addition was found to be vital in improving materials’ catalytic performance through preventing aggregation of the nanospheres, constructing porous structures, increasing the surface area, and participating in the formation of active sites.
A high-performance doped carbon catalyst with a BET surface area of up to 949 m2 g−1 has been prepared by pyrolyzing soybean biomass with ZnCl2 as an activator, followed by acid leaching with H2SO4 ...and graphitization. For the cathodic reduction of oxygen, the catalyst exhibits excellent activity in an alkaline medium. Its onset potential and half-wave potential for the oxygen reduction reaction reach −0.02 V and −0.12 V (vs. Ag/AgCl) in 0.1 M KOH, almost comparable to those of commercial 20 wt% Pt/C catalyst. It is found that the addition of zinc chloride can significantly enhance the catalyst's surface area and activity. We suggest that the high performance of this type of catalyst is mainly contributed from its high active center density resulted from the high surface area of the catalyst, which is caused by the activation of zinc chloride.
A novel high-performance, biomass-derived, carbon-based catalyst, with a BET surface area of up to 949 m2 g−1, has been prepared for the first time by pyrolyzing soybean biomass impregnated with a chemical activator, followed by acid leaching and graphitization. For the cathodic reduction of oxygen, the catalyst exhibits excellent activity in an alkaline medium, almost comparable to the performance of commercial 20 wt% Pt/C catalyst. Display omitted
•A novel biomass-derived doped carbon catalyst is prepared using soybean as precursor.•The catalyst exhibited high ORR activity comparable to Pt/C in an alkaline medium.•The addition of ZnCl2 enhanced the surface area and performance of the catalyst.
In an air-breathing proton exchange membrane fuel cell (ab-PEMFC), large amounts of water are generated and condensed on the cathode at high current densities due to the low operating temperature. ...Water management for ab-PEMFCs remains a challenge. In this paper, a cathode with a dual catalyst layer structure is designed, and the gas diffusion layer (GDL) and microporous layer (MPL) are optimized to improve the water management of an ab-PEMFC. A thin hydrophilic layer using perfluorosulfonate (Nafion) as the catalyst binder is coated on the electrolyte membrane to form an inner layer that maintains a good proton transfer rate, while a hydrophobic outer layer is prepared using a mixture of Nafion and polytetrafluoroethylene as the binder, preventing the removal of water under low-humidity conditions and expelling the excess water generated in the high current density area. A membrane electrode assembly (MEA) with this dual catalyst layer cathode exhibits excellent air-breathing performance, as the MEA's water management is greatly improved by the dual layer structure. We also find that the thickness of the MPL and the hydrophobicity of the GDL significantly affect the air-breathing performance of the MEA, and we attempt to optimize these parameters.
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•A dual catalyst layer cathode is designed for water management of ab-PEMFCs.•The cathode is composed of a hydrophilic inner layer and hydrophobic outer layer.•The GDL composition affects the performance of the ab-PEMFC significantly.•The ab-PEMFC with the dual catalyst layer cathode exhibits excellent performance.
Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition ...metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (2
P
-Fe
-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl
as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.
Phase change materials (PCMs) are widely used to improve energy utilization efficiency due to their high energy storage capacity. In this study, double-shell microencapsulated PCMs were constructed ...to resolve the liquid leakage issue and low thermal conductivity of organic PCMs, which also possess high thermal stability and multifunctionality. We used assembly to construct an inorganic-organic double shell for microencapsulate PCMs, which possessed the unprecedented synergetic properties of a cadmium sulfide (CdS) shell and melamine-formaldehyde polymeric shell. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirmed the well-designed double-shell structure of the microcapsules, and the CdS was successfully assembled as the second shell on the surface of the polymer shell. The differential scanning calorimeter (DSC) showed that the double-shell microcapsules had a high enthalpy of 114.58 J/g, which indicated almost no changes after experiencing 100 thermal cycles, indicating good thermal reliability. The microcapsules also showed good shape stability and antileakage performance, which displayed no shape change and leakage after heating at 60 °C for 30 min. In addition, the photothermal conversion efficiency of the double-shell microcapsules reached 91.3%. Thus, this study may promote the development of microencapsulated PCMs with multifunctionality, offering considerable application prospects in intelligent temperature management for smart textiles and wearable electronic devices in combination with their solar thermal energy conversion and storage performance.
A novel core–shell structured catalyst, Ir@Pt/C, was prepared by a facile pulse electrochemical deposition approach, demonstrating several times higher mass activity towards both the anodic oxidation ...of methanol and the cathodic reduction of oxygen than commercial Pt/C catalyst. And the results of CO stripping revealed that the Ir@Pt/C catalyst exhibited greater ease of CO removal. The enhanced performance of the catalyst could be ascribed to the high dispersion of Pt, which led to the higher utilization of Pt, and the synergetic effect of Pt with Ir in the core–shell structure.
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•Core–shell Ir@Pt/C catalyst is prepared by pulse electrochemical deposition method.•The catalyst exhibits ultra high Pt dispersion with shell thickness of ca. 1.0nm.•The oxidation potential of CO on the catalyst is 108mV lower than that of Pt/C.•The Pt mass activity of the catalyst towards MOR and ORR is enhanced by three times.
Non-noble metal electrocatalysts for oxygen reduction reaction are essential for the sustainability and cost reduction of energy conversion devices. However, the performance of non-noble metal ...catalysts is far inferior to that of platinum-based catalysts. It remains a challenge to synthesize high-performance non-noble metal catalysts using simple methods. Iron and copper are the core elements of hemoglobin and hemocyanin, which are the main components of oxygen carried in animals. Based on the above inspiration, a novel Fe and Cu bimetallic mixed porous carbon material was synthesized by a one-step method. Our catalyst Fe-Cu–N/C-F-1.5 had a porous structure, and its specific surface area is 625 m
2
g
−1
. Fe–Cu–N/C–F-1.5 exhibited an excellent electrochemical characteristic with an initial potential of 0.98 V and a half-wave potential of 0.85 V, which could achieve better electrochemical activity than commercial Pt/C. This work provides a general approach for the rational design of transition metal and heteroatom mixed porous carbon electrocatalysts.
Graphical abstract
A Fe- and Cu-doped carbon catalyst, Fe–Cu–N/C–F-1.5, is prepared from melamine, polytetrafluoroethylene (PTFE), and FeCl
3
, (CH
3
COO)
2
Cu•H
2
O by a one-pot method. Fe–Cu–N/C–F-1.5 with a porous structure and its specific surface area is 625 m
2
g
−1
. Fe–Cu–N/C–F-1.5 shows good catalytic performance in ORR processes. The ORR half-wave potential of Fe–Cu–N/C–F-1.5 is positively shifted by 35 mV compared with that of commercial Pt/C.
The rapid development of industry has emphasized the importance of phase change materials (PCMs) with a high latent-heat storage capacity and good thermal stability in promoting sustainable energy ...solutions. However, the inherent low thermal conductivity and poor thermal-cycling stability of PCMs limit their application. In this study, we constructed three-dimensional (3D) hybrid graphene aerogels (GBA) based on synergistic assembly and cross-linking between GO and modified hexagonal boron nitride (h-BN). Highly thermally conductive GBA was utilized as the supporting optimal matrix for encapsulating OD, and further implied that composite matrix n-octadecane (OD)/GBA composite PCMs were further prepared by encapsulating OD within the GBA structure. Due to the highly thermally conductive network of GBA, the latent heat of the composite PCMs improved to 208.3 J/g, with negligible changes after 100 thermal cycles. In addition, the thermal conductivity of the composite PCMs was significantly enhanced to 1.444 W/(m·k), increasing by 738% compared to OD. These results sufficiently confirmed that the novel GBA with a well-defined porous structure served as PCMs with excellent comprehensive performance offer great potential for thermal energy storage applications.
