Direct synthesis of nitrogen and phosphorus co-doped hierarchical porous carbon networks with biological materials as efficient electrocatalysts for oxygen reduction reaction

We described a process of the preparation of N, P co-doped hierarchical porous carbon by one-step pyrolysis of the chitosan/phytic acid (CS/PA) precursor without extra activation processes, and the nitrogen and phosphorus were successfully incorporated into the carbon framework. Experimentally, the best performance was identified with NPC-1000 which possessed the highest BET specific surface area of 1117.2 m² g^?1. This NPC-1000 showed a half-wave potential of 50 mV difference with commercial Pt/C, better tolerance to methanol and a superior stability comparable to commercial Pt/C catalyst. The results suggest that it is a simple, feasible, and economical route to synthesis of hierarchical porous carbon which can be used as metal-free catalysts for oxygen reduction.     

Facile synthesis of efficient core-shell structured iron-based carbon catalyst for oxygen reduction reaction

Controlled synthesis of efficient core-shell non-precious metal catalysts for oxygen reduction reaction (ORR) is undoubtedly crucial but challenging for the extensive application of fuel cells and metal-air batteries. Herein, we prepared a core-shell structured Fe/FeC_x nanoparticles and porous carbon composited catalyst (Fe/FeC_x@NC) via a facile two-step heat treatment strategy. The Fe/FeC_x@NC-800_?0.5 prepared with secondary anneal at 800 °C for 0.5 h exhibits superior ORR performance to the commercial Pt/C in terms of comparable onset potential, higher half-wave potential, and outstanding long-term durability in alkaline media. Through combining the physical and electrochemical characterizations of Fe/FeC_x@NC-T_?t with different anneal temperature and precursors, the outstanding ORR performance of Fe/FeC_x@NC-800_?0.5 is caused by the synergistic effect between Fe/FeC_x core and enriched pyridinic N- and graphitic N-doped carbon shell as well as porous carbon with large specific surface area. The structure-activity relationship of core-shell structured Fe–N–C catalysts for ORR provides directions for the development of advanced nonprecious metals catalysts.     

Improvement in the durability of carbon black-supported Pt cathode catalysts by silica-coating for use in PEFCs

Commercially available Pt metal catalysts supported on carbon black (Pt/CB) for polymer electrolyte fuel cell (PEFC) cathodes were covered with silica layers to improve their durability under the severe cathode operating conditions. The Pt metal particles in the Pt/CB catalyst grew in size during the accelerated durability tests (potential cycling between 0.6 and 1.0 V vs. RHE in an aqueous HClO₄ electrolyte). Thus, the Pt/CB catalyst was seriously deactivated for the oxygen reduction reaction over the course of the durability tests. In contrast, the silica layers, which wrapped around the Pt metal particles in the silica-coated Pt/CB catalyst, prevented the migration of the Pt metal particles on the carbon supports and the diffusion of Pt cations out of the silica layers. Thus, the silica-coated Pt/CB catalysts maintained a high activity for the oxygen reduction reaction over the course of the durability tests. In addition, the silica-coated Pt/CB prepared from methyltriethoxysilane showed a higher activity than that prepared from tetraethoxysilane. The porous structures and hydrophobicity of silica prepared from methyltriethoxysilane promoted the diffusion of oxygen and water molecules in the silica layers of the silica-coated Pt catalysts.     

Iron and nitrogen codoped carbon catalyst with excellent stability and methanol tolerance for oxygen reduction reaction

A series of non‐precious metal Fe_xNC electrocatalysts for oxygen reduction reaction (ORR) were successfully synthesized using Fe(NO₃)₃, glucose, and melamine as the Fe, C, and N sources, respectively. The effects of the pyrolysis temperature and Fe/N contents on the catalytic performances are comprehensively investigated. Electrochemical results reveal that among the Fe_xNC catalysts, Fe_1.5NC‐900‐2 pyrolyzed at 900°C with the mass ratio of FeC to melamine being 1:10 proves the highest catalytic performance. The half‐wave potential (E_1/2) of ORR was 821 mV (vs reversible hydrogen electrode (RHE)) and only 36 mV lower than that on commercial Pt/C catalyst (857 mV). More importantly, Fe_1.5NC‐900‐2 catalyst shows excellent stability and methanol tolerance. After 1000 sequential cycles, the E_1/2 on Pt/C catalyst shifts negatively by approximately 60 mV, while for Fe_1.5NC‐900‐2 catalyst, this shift is only 28 mV although the number of sequential cycles is increased to 8000. In the presence of methanol, the current decay in the chronoamperometric response at 1000 seconds is only 8% and also much lower than that on Pt/C catalyst (46%). The high catalytic performances arise from the abundant Fe₃N active sites embedded in the carbon matrix of the Fe_xNC catalysts. These findings can be used to discuss the catalytic mechanism of ORR on the Fe_xNC catalysts and design the nonprecious metal carbon‐based electrocatalysts for ORR.     

Eutectic salts assisted synthesis of MOF-derived porous carbon as Pt–Sn catalyst support for ethanol oxidation reaction

The development of ethanol oxidation reaction (EOR) catalysts with high performance is an emerging need of direct ethanol fuel cells (DEFCs). Rational design of support materials of platinum-based catalyst can significantly enhance its catalytic performance for EOR. Here, the highly porous nitrogen-doped carbon material (NC-E) from ZIF-8 was synthesized using a novel and simple method assisted by eutectic salts. Compared with the carbon material obtained from ZIF-8 by traditional calcination (NC-T) and carbon black, the NC-E with high surface area and hierarchical pore structure supported Pt–Sn catalyst exhibits improved electrochemical activity and stability.     

Rapeseed meal-based autochthonous N and S-doped non-metallic porous carbon electrode material for oxygen reduction reaction catalysis

The heteroatom-doped porous carbon material as an alternative to commercial Pt/C catalysts in oxygen reduction reaction has attracted extensive attention. In this study, the rapeseed meal-based material (ARM-900) prepared by carbonization with high temperature and activation with ZnCl₂ had a porous structure and was doped with N and S heteroatoms. Compared to commercial Pt/C catalysts (onset potential of 0.95 V vs. RHE and limiting diffusion current of ?5.7 mA cm^?2), ARM-900 demonstrated excellent electrocatalytic performance with an onset potential of 0.98 V vs. RHE and limiting diffusion current of ?8.1 mA cm^?2 in O₂ saturated 0.1 M KOH solution. Meanwhile, ARM-900 had higher durability and more superior methanol tolerance than Pt/C catalyst. The excellent ORR performance of ARM-900 was derived from the formation of abundant pore structure and the doping of the autochthonous N and S heteroatoms. MFCs with ARM-900 as the cathode had the maximum power density of 808 mW/m², which was obviously better than Pt/C (709 mW/m²). This study provided an environment-friendly and effective strategy for the reuse of rapeseed meal and the preparation of N and S-doped non-metallic ORR catalysts.     

One-step complexation and self-template strategy to synthesis bimetal Fe/Mn–N doped interconnected hierarchical porous carbon for enhancing catalytic oxygen reduction reaction

Currently, it is still a challenge in the research of fuel cells and zinc-air battery to use a facile method to prepare efficient and low-cost cathode oxygen reduction reaction (ORR) catalysts to replace the precious metal Pt-based catalyst. Herein, we reported a one-step complexation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) with transition metals (M) and self-template strategy to synthesis an bimetal Fe/Mn–N doped interconnected hierarchical porous carbon material for efficient catalytic ORR. In addition to being a carbon source, EDTA-2Na can very well fix M atoms in the carbon precursory by complexation, which is beneficial for M atoms to be anchored in the carbon structure by N atoms, thus forming the M-N_x catalytic active site. During pyrolysis, meanwhile, Na ions in EDTA-2Na not only acted as self-template to form the interconnected porous structure but also separated M atoms from each other, which also suppressed the aggregation and growth of the M atoms. More importantly, the prepared bimetal Fe/Mn–N doped interconnected hierarchical porous carbon (Fe/Mn–NIHPC) showed better catalytic ORR performance (half-wave potentials of 0.86 V vs. RHE) than those prepared by single metal elements (Fe or Mn). And Fe/Mn–NIHPC also exhibited better catalytic ORR activity and durability, compared with the Pt/C (20 wt%) catalyst.     

Influence of support’s oxygen functionalization on the activity of Pt/carbon xerogels catalysts for methanol electro-oxidation

Highly mesoporous carbon xerogels (CXs) were synthesized using two different resorcinol to catalyst, R/C, molar ratios and functionalized with different oxidation treatments. The synthesized carbon materials were used as supports for Pt particles, deposited by impregnation and reduction in formic acid. Both carbon supports and the catalysts prepared were characterized by means of N₂ physisorption, scanning and transmission electron microscopy, temperature programmed desorption and X-ray diffraction. The electrochemical activity of the catalysts towards the oxidation of carbon monoxide and methanol was assayed by means of cyclic voltammetry and chronoamperometry. Textural characterization of the materials prepared evidenced more developed and mesopore-enriched porous structure for the carbon xerogel prepared using the highest R/C molar ratio. Enhanced textural properties of this material led to the preparation of highly active Pt-catalysts, which showed increased tolerance to CO and higher activity in methanol electro-oxidation, in comparison to Pt-E-TEK and the catalysts prepared in an analogous way using Vulcan XC-72R carbon black as support. Functionalization treatments resulted in enhanced dispersion, lower Pt crystal size and improved catalytic performance in the case of the catalysts prepared using the carbon xerogel possessing a less developed porous structure. Pt agglomeration was found to strongly determine the activity of the catalysts prepared. At high potentials, i.e. 1 V vs. RHE, the catalyst prepared using the carbon xerogel submitted to the most stringent oxidation treatment showed the highest specific peak activity towards methanol electro-oxidation, probably due to the positive influence of the presence of oxygen surface groups in Pt-carbon interaction, in spite of the higher agglomeration extent confirmed by TEM. On the other hand, at 0.60 V vs. RHE, highest activity towards methanol electro-oxidation was determined for the catalysts prepared using the non-functionalized carbon xerogel which can be explained in terms of enhanced reactant/product diffusion together with intrinsic higher catalytic activity due to lower Pt crystal size. In any case, the activity of this catalyst prepared using a carbon xerogel as support was found to be more than 2 times higher than the one determined for Pt/E-TEK, confirming the considerable improvement of the electrocatalytic system by means of optimization of the carbon support employed.     

High-performance N,P-CNL nanocomposites as catalyst for oxygen reduction reaction in fuel cell

Transition metal and heteroatom codoped carbon materials have become the most promising materials to replace commercial platinum carbon (Pt / C) catalysts due to their low cost, high stability, and methanol resistance. In this work, iron-nitrogen and phosphorus codoped carbon nanorod-layer composites (N, P-CNL) derived from phosphorus-doped polyaniline (P-PANI) by phytic acid (PA) and iron salt were successfully obtained after high-temperature pyrolysis. As a result, the N, P-CNL materials exhibited good electrocatalytic performance due to abundant active sites. The N, P-CNL with 50% mass filling ratio of iron salt (named as N, P-CNL-1:1) displayed an enhanced limiting current density of −5.97 mA cm⁻² at 1600 rpm and outstanding onset potential (−0.004 V) and oxygen reduction peak potential (−0.144 V). In general, this work can give insights into understanding the mechanism of codoped catalysts and synthesis the catalyst with excellent long-term stability and resistance to methanol crossover and poisoning better than commercial Pt/C.     

Spillover enhanced hydrogen uptake of Pt/Pd doped corncob-derived activated carbon with ultra-high surface area at high pressure

Corncob-derived activated carbon (CAC) was prepared by potassium hydroxide activation. The Pt/Pd-doped CAC samples were prepared by two-step reduction method (ethylene glycol reduction plus hydrogen reduction). The as-obtained samples were characterized by N₂-sorption, TEM and XRD. The results show the texture of CAC is varied after doping Pt/Pd. The Pd particles are easier to grow up than Pt particles on the surface of activated carbon. For containing Pt samples, the pore size distributions are different from original sample and Pd loaded sample. The hydrogen uptake results show excess hydrogen uptake capacity on the Pt/Pd-doped CAC samples are higher than pure CAC at 298 K, which should be attributed to hydrogen spillover effects. The 2.5%Pt and 2.5%Pd hybrid doped CAC sample shows the highest hydrogen uptake capacity (1.65 wt%) at 298 K and 180 bar, The particle size and distribution of Pt/Pd catalysts could play a crucial role on hydrogen uptake by spillover. The total hydrogen storage capacity analysis show that total H₂ storage capacities for all samples are similar, and spillover enhanced H₂ uptakes of metal-doped samples could not well support total H₂ storage capacity. The total pore volume of porous materials also is a key factor to affect total hydrogen storage capacity.     

An efficient Co-N/C electrocatalyst for oxygen reduction facilely prepared by tuning cobalt species content

Transition metal and nitrogen co-doped carbon catalysts for the oxygen reduction reaction (ORR) have emerged as promising candidates to replace the expensive platinum catalysts but still remain a great challenge. Herein, a novel and efficient nitrogen-doped carbon material with metal cobalt co-dopant (Co–N/C) has been prepared by pyrolyzing porphyrin-based covalent organic polymer where Co is anchored. The optimized 10%-Co-N/C catalyst through facilely and efficiently tuning the cobalt content is carefully characterized by XRD, Raman, XPS, SEM and TEM for composition and microstructure analysis. This catalyst with only 0.56% Co exhibits an excellent ORR catalytic activity with a positive half-wave potential of 0.816 V (vs. RHE) in 0.1 M KOH solution, which is comparable to that of commercial Pt/C (20 wt%). Notably, the 10%-Co-N/C catalyst displays better electrochemical stability with only a loss of 5.1% of its initial current density in chronoamperometric measurement and also gives rise to stronger methanol tolerance than Pt/C. The good ORR catalytic behaviour for this catalyst may be attributed to the dispersion of the Co-N_X active sites via adjusting the contents of cobalt species in porous organic framework.     

Effect of pretreatment on Pt–Co/C cathode catalysts for the oxygen reduction reaction

Carbon supported Pt and Pt–Co electrocatalysts for the oxygen reduction reaction in low temperature fuel cells were prepared by the reduction of the metal salts with sodium borohydride and sodium formate. The effect of surface treatment with nitric acid on the carbon surface and Co on the surface of carbon prior to the deposition of Pt was studied. The catalysts where Pt was deposited on treated carbon the ORR reaction preceded more through the two electron pathway and favored peroxide production, while the fresh carbon catalysts proceeded more through the four electron pathway to complete the oxygen reduction reaction. NaCOOH reduced Pt/C catalysts showed higher activity that NaBH₄ reduced Pt/C catalysts. It was determined that the Co addition has a higher impact on catalyst activity and active surface area when used with NaBH₄ as reducing agent as compared to NaCOOH.     

Boron doping induced electronic reconfiguration of Fe-Nx sites in N-doped carbon matrix for efficient oxygen reduction reaction in both alkaline and acidic media

Developing non-precious metal-based catalysts as the substitution of precious catalysts (Pt/C) in oxygen reduction reaction (ORR) is crucial for energy devices. Herein, a template and organic solvent-free method was adopted to synthesize Fe, B, and N doped nanoflake-like carbon materials (Fe/B/N–C) by pyrolysis of monoclinic ZIF-8 coated with iron precursors and boric acid. Benefiting from introducing B into Fe–N–C, the regulated electron cloud density of Fe-N_x sites enhance the charge transfer and promotes the ORR process. The as-synthesized Fe/B/N–C electrocatalyst shows excellent ORR activity of a half-wave potential (0.90 V vs 0.87 V of Pt/C), together with superior long-term stability (95.5% current density retention after 27 h) in alkaline media and is even comparable to the commercial Pt/C catalyst (with a half-wave potential of 0.74 V vs 0.82 V of Pt/C) in an acidic electrolyte. A Zn-air battery assembled with Fe/B/N–C as ORR catalyst delivers a higher open-circuit potential (1.47 V), specific capacity (759.9 mA h g^?1_Zn at 10 mA cm^?2), peak power density (62 mW cm^?2), as well as excellent durability (5 mA cm^?2 for more than 160 h) compared to those with commercial Pt/C. This work provides an effective strategy to construct B doped Fe–N–C materials as nonprecious ORR catalyst. Theoretical calculations indicate that introduction of B could induce Fe-N_x species electronic configuration and is favorable for activation of OH1 intermediates to promote ORR process.     

Three-dimensional porous PtCu as highly efficient electrocatalysts for methanol oxidation reaction

Exploring affordable, durable, and effective electrocatalysts for methanol oxidation reaction (MOR) is of great importance to the industrial application of direct methanol fuel cells. Herein, a three-dimensional (3D) porous PtCu catalyst is synthesized by a facile and effective galvanic replacement method, which exhibits high activity and durability for MOR. The modulated electronic and strain effects of the Pt atoms are verified by extensive characterizations, and the mass and specific activities of the prepared catalyst are roughly 3.8 and 9.9 times higher than those of the commercial Pt/C catalysts, respectively. The robust activity of the prepared catalyst is probably owing to the optimized affination between Pt and the adsorbed poisoning species (mainly CO) induced by the electronic and strain effects of the Pt, as well as the unique 3D porous nanostructure.     

Preparation and characterization of nanoporous carbon-supported platinum as anode electrocatalyst for direct borohydride fuel cell

The nanoporous carbon (NPC) is synthesized by carbonization of metal–organic framework-5 (MOF-5, [Zn₄O(bdc)₃], bdc = 1,4-benzenedicarboxylate) with furfuryl alcohol (FA) as carbon source and used as the carrier of the anode catalyst for the direct borohydride–hydrogen peroxide fuel cell (DBHFC). Then the NPC-supported Pt anode catalyst (Pt/NPC) is firstly prepared by a modified NaBH₄ reduction method. The obtained Pt/NPC catalyst is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), cyclic voltammetry, chronopotentiometry, chronoamperometry and fuel cell test. The results show that the Pt/NPC is made up of the spherical Pt nanoparticles which disperse uniformly on the surface of the NPC with average size 2.38 nm, and exhibits 36.38% higher current density for directly borohydride oxidation than the Vulcan XC-72 carbon supported Pt (Pt/XC-72). Besides, the DBHFC using the Pt/NPC as anode electrocatalyst shows the maximum power density as high as 54.34 mW cm⁻² at 25 °C.     

The role of arginine as nitrogen doping and carbon source for enhanced oxygen reduction reaction

Doped carbon nanostructures as non-precious metal (NPM) catalysts for oxygen reduction reaction (ORR) in acid medium are mainly synthesized using 5, 10, 15, 20-tetrakis (4-methoxyphenyl)-porphyrin-Fe (III) chloride (Fe-TMPP) as doping and carbon sources. In this study, the doped carbon nanostructures used as cathode NPM catalysts for ORR are prepared using a mixture of iron phthalocyanine (FePc) and arginine as doping and carbon sources. The morphology and composition of the as-prepared samples are characterized using field-emission scanning electron microscopy, field-emission transmission electron microscopy, and energy dispersive X-ray (EDX) spectroscopy. The crystal and pore structures are analyzed using X-ray diffraction method, Raman spectroscopy, and nitrogen adsorption/desorption method. The sample prepared using a precursor mixture with a proper ratio of FePc and arginine exhibits significantly superior ORR performance, i.e. high specific activity, enhanced half-wave potential, and improved stability in an acid medium, as even compared to a commercial Pt/C. The improved ORR properties is mainly attributed to high portion of pyridinic N state with a relatively high specific surface area, which can result from the FePc precursor surrounded by the fused arginine.     

Pt electrodeposited on CeZrO4/MCNT as a new alternative catalyst for enhancement of ethanol oxidation

Electrocatalytic preparation of Pt-based nanocomposites has been investigated for improvement of direct ethanol fuel cells (DEFCs). In this study, new alternative catalysts of Pt-decorated cerium zirconium oxide-modified multiwalled carbon nanotubes (Pt/CeZrO₄/MCNT) were successively prepared to improve the activity of the ethanol oxidation reaction (EOR). The prepared CeZrO₄ with a face-centered cubic (fcc) structure compatibly dispersed onto MCNT provides abundant active Pt sites for highly active catalysts. The fcc-structured Pt was also satisfactorily decorated onto CeZrO₄/MCNT, resulting in highly active Pt. The Ce⁴⁺/Ce³⁺ redox property can promote oxygen vacancies to improve the electrochemical activity for oxidation of carbonaceous species. An increase in roughness and a stabilized catalyst structure can also be produced by inserting Zr⁴⁺ into the ceria metal oxide. The prepared Pt/20%CeZrO₄/MCNT catalysts present excellent electrochemical active surface area, mass activity, CO tolerance and high electron kinetic transfer with low resistance and high stability over commercial PtRu/C toward EOR. This promising catalyst material could be introduced to enhance the anodic oxidation reaction in DEFCs.     

Promising nature-based nitrogen-doped porous carbon nanomaterial derived from borassus flabellifer male inflorescence as superior metal-free electrocatalyst for oxygen reduction reaction

In this present study, novel hierarchical nitrogen-doped porous carbon for use as a metal-free oxygen reduction reaction (ORR) electrocatalyst is derived from borassus flabellifer male inflorescences by calcining at 1000 °C in an inert atmosphere using metal hydroxides as activating agent and melamine as nitrogen doping agent. The BET surface areas of the lithium-ion (Li-ion), potassium-ion (K-ion) and calcium-ion (Ca-ion) activated carbon are observed to be 824.02, 810.88 and 602.88 m² g^-1 respectively. Another interesting fact is that the total surface energy calculated by wicking method (73.2 mJ/m²), is found to be higher for Li-ion activated carbons. Among the prepared nitrogen-doped porous carbon, Li-ion activated system, showed an outstanding performance in ORR reaction in alkaline medium, thanks to its high surface area and notable surface activity. An incontrovertible of note that ORR half-wave potential of Li-ion activated nitrogen-doped carbon (0.90 V) is relatively higher in comparison to the commercial 20 wt % Pt/C catalyst (0.86 V). Inspite of overwhelming performance, the ORR reaction followed the preferred 4- electron transfer mechanism involving in the direct reduction pathway in all activated carbons. The ORR performance is also noticeably better and comparable to the best results in the literature based on biomass derived carbon catalysts.     

One-step synthesis of Co2P/N-P co-doped porous carbon composites derived from soybean derivatives as acidic and alkaline HER electrocatalysts

Developing inexpensive and efficient electrocatalysts for hydrogen evolution reaction (HER) in both acidic and alkaline mediums is of great significance to the hydrogen energy industry. Hereby, we prepared a mixture of precursors with homogeneous composition by using the chelating ability of soybean protein isolate (C and N source) and phytic acid (dopant and phosphating agent) with cobalt ions, and achieved one-step synthesis and construction of Co₂P/N–P co-doped porous carbon composite by carbonization at 800 °C. The as-synthesized Co₂P/NPPC-800 electrocatalyst exhibits low HER overpotentials of 121 and 125 mV at 10 mA cm^?2 in 0.5 M H₂SO₄ and 1.0 M KOH, which are close to those of the commercial Pt/C catalyst. Additionally, the NPPC substrate surrounding the Co₂P could diminish the corrosion during the HER, and Co₂P/NPPC-800 displays good stability and durability. Furthermore, this work offers a convenient synthesis strategy for phosphide/doped porous carbon composites in other electrochemical energy technologies.     

Sewage sludge-derived Fe- and N-containing porous carbon as efficient support for Pt catalyst with superior activity towards methanol electrooxidation

In this work, a facile Fe- and N-containing porous carbon derived from sewage sludge was prepared and served as the support of Pt nanoparticles for the electrooxidation of methanol. Both the sludge-derived carbon (denoted as SC) and the resultant Pt/SC catalyst was physically characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The electrocatalytic performance for methanol oxidation reaction (MOR) of the Pt/SC was examined by cyclic voltammetry (CV) and chronoamperometric method. The results showed that the Pt/SC possessed slightly larger Pt particle size (5.5 nm) and lower electrochemical active surface area (ECA) compared to common Pt/C catalyst. However, the mass activity of Pt/SC for MOR was up to 201 mA mg⁻¹, which was much higher than that of Pt/C (93 mA mg⁻¹), indicating the synergistic effect of the sewage sludge-derived carbon with Fe and N species on methanol electrooxidation. Furthermore, Pt/SC showed enhanced durability towards MOR compared to common Pt/C, implying its potential for using in direct methanol fuel cell (DMFC) for energy conversion, which also demonstrated a promising solution for the utilization of sewage sludge resources.