Novel dual templating approach for preparation of highly active Fe-N-C electrocatalyst for oxygen reduction

Mesoporous Metal Nanomaterials: Developments and Electrocatalytic Applications

Mesoporous metal nanomaterials (MPMNs) are pivotal in nanotechnology, especially in electrochemical applications, due to their unique structure. Unlike traditional nanomaterials, MPMNs possess hierarchical and mesoporous characteristics, providing more active sites for improved mass and electron transfer. This distinctive composition offers dual benefits, enhancing activity, stability, and selectivity for specific reactions. The intricate architecture, featuring interconnected pores, amplifies surface area, ensuring efficient use of active sites and boosting reactivity in electrocatalytic processes. Additionally, the mesoporous nature promotes superior diffusion kinetics, facilitating better transport of reactants and products. This intricate interplay of structural elements contributes not only to the increased efficiency of electrochemical reactions but also to the extended durability of MPMNs during prolonged usage. This concept focus on the synthesis and design strategies of MPMNs, aligning with the dynamic requirements of diverse electrocatalytic applications. The synergy resulting from these advancements not only accentuates the intrinsic properties of MPMNs but also broadens their scope for practical implementation in emerging fields of electrochemistry.

Pt/Pd Decorate MOFs Derived Co-N-C Materials as High-Performance Catalysts for Oxygen Reduction Reaction

We report here, a strategy to prepare Pt/Pd nanoparticles decorated with Co-N-C materials, where Co-N-C was obtained via pyrolysis of ZIF-67 directly. As-prepared Pt/Pd/Co-N-C catalysts showed excellent ORR performance, offered with a higher limit current density (6.6 mA cm−2) and similar half-wave potential positive (E1/2 = 0.84 V) compared with commercial Pt/C. In addition to an ORR activity, it also exhibits robust durability. The current density of Pt/Pd/Co-N-C decreased by only 9% after adding methanol, and a 10% current density loss was obtained after continuous testing at 36,000 s.

Highly active iron-nitrogen-boron-carbon bifunctional electrocatalytic platform for hydrogen peroxide sensing and oxygen reduction

An iron-nitrogen-boron-carbon (Fe-N-B-C) bifunctional electrocatalyst was prepared by means of a facile one-step hydrothermal reduction of graphene oxide using dimethylamine borane as doping agent. In addition, hemins were efficiently anchored during doping/reducing process on this modified graphene. The as-prepared Fe-N-B-C electro-catalyst showed enhanced response as regards its potential for reduction of H₂O₂ and O₂. In view of its catalytic activity, this Fe-N-B-C material was tested for the determination of H₂O₂ with a chronoamperometry method, obtaining a detection limit as low as 0.055 μM, which is better than that of some Hemin-N-C materials. Regarding O₂ reduction reaction, a study performed using a rotating disk electrode indicated that this material exhibits a positive onset potential (0.90V vs. RHE), high selectivity (4e^- process), high limiting-current density (4.75 mA cm^-2) and strong resistance against the crossover-effect from methanol in alkaline medium, making it to be the promising candidate as alternative for commercial Pt/C catalysts. These results could have commercial and environmental relevance and would deserve further complementary investigation.

Facile Synthesis of MoP-RuP2 with Abundant Interfaces to Boost Hydrogen Evolution Reactions in Alkaline Media

Exploiting efficient electrocatalysts for hydrogen evolution reactions (HERs) is important for boosting the large-scale applications of hydrogen energy. Herein, MoP-RuP₂ encapsulated in N,P-codoped carbon (MoP-RuP₂@NPC) with abundant interfaces were prepared via a facile avenue with the low-toxic melamine phosphate as the phosphorous resource. Moreover, the obtained electrocatalyst possessed a porous nanostructure, had abundant exposed active sites and improved the mass transport during the electrocatalytic process. Due to the above merits, the prepared MoP-RuP₂@NPC delivered a greater electrocatalytic performance for HERs (50 mV@10 mA cm⁻²) relative to RuP₂@NPC (120 mV) and MoP@NPC (195 mV) in 1 M KOH. Moreover, an ultralow potential of 1.6 V was required to deliver a current density of 10 mA cm⁻² in the two-electrode configuration for overall water splitting. For practical applications, intermittent solar energy, wind energy and thermal energy were utilized to drive the electrolyzer to generate hydrogen gas. This work provides a novel and facile strategy for designing highly efficient and stable nanomaterials toward hydrogen production.

Development of a highly active FeNC catalyst with the preferential formation of atomic iron sites for oxygen reduction in alkaline and acidic electrolytes

Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesizedviacomplicated routes involving multiple heat-treatment steps to form the desired Fe-N_x sites. We herein developed a highly active FeNC catalyst comprising of exclusive Fe-N_x sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-N_x centers, which yielded a high density of electrochemically accessible active sites (1.36 × 10¹⁹ sites g^-1) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E_1/2) of 0.905 V_RHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E_1/2 of 0.760 V_RHE is achieved at a low loading level (0.29 mg cm^-2). In PEMFC tests, a current density of 2.3 mA cm^-2 is achieved at 0.90 V_iR-free under H₂-O₂ conditions, reflecting high kinetic activity of the optimized catalyst.

N-Doped porous tremella-like Fe3C/C electrocatalysts derived from metal–organic frameworks for oxygen reduction reaction

A tremella-like porous Fe₃C/C nanocomposite derived from metal–organic frameworks shows improved oxygen reduction reaction performance.

A Lactate/Oxygen Biofuel Cell: The Coupled Lactate Oxidase Anode and PGM-Free Fe-N-C Cathode

The rapid development of both wearable and implantable biofuel cells has triggered more and more attention on the lactate biofuel cell. The novel lactate/oxygen biofuel cell (L/O-BFC) with the direct electron transfer (DET)-type lactate oxidase (LOx) anode and the platinum group metal (PGM)-free Fe-N-C cathode is designed and constructed in this paper. In such a reasonable design, the surface-controlled direct two-electron electrochemical reaction of the lactate oxidase was determined by cyclic voltammetry (CV) on the carbon nanotube (CNT) modified electrode with favorable high electrochemical active surface area and electronic conductivity. Additionally, the biosensor based on DET-type LOx modified electrode impressively presented linear response to lactate with different concentrations from 0.000 mM to 12.300 mM. In particular, the apparent Michealis-constant (K_M^app) calculated as 0.140 mM clearly indicates that LOx on CNT has strong affinity to the substrate lactate. Meanwhile, 4e^- transfer oxygen reduction reaction (ORR) was proven to take place on the Fe-N-C catalysts inthe 0.1 M PBS system, indicating the advantage by using the Fe-N-C catalysts at the cathode of L/O-BFC. Last but not least, the L/O-BFC with the direct electron transfer (DET)-type lactate oxidase(LOx) anode and the Fe-N-C cathode produced an superior open circuit potential (OCP) of 0.264 V and a maximum output power density (OPD) of 24.430 μW cm^-2 in O₂ saturated 95.020 mM lactate solution. The above results will not only bring about significant interest in developing a DET-type biofuel cell, but also offer guiding direction to explore novel catalyst materials for the biofuel cell. This work enriches the research content and may push developments of the implantable and wearable biofuel cell forward.

Tunable Synthesis of Hollow Metal-Nitrogen-Carbon Capsules for Efficient Oxygen Reduction Catalysis in Proton Exchange Membrane Fuel Cells

Atomically dispersed metal catalysts anchored on nitrogen-doped (N-doped) carbons demand attention due to their superior catalytic activity relative to that of metal nanoparticle catalysts in energy storage and conversion processes. Herein, we introduce a simple and versatile strategy for the synthesis of hollow N-doped carbon capsules that contain one or more atomically dispersed metals (denoted as H-M-N_x-C and H-M^mix-N_x-C, respectively, where M = Fe, Co, or Ni). This method utilizes the pyrolysis of nanostructured core-shell precursors produced by coating a zeolitic imidazolate framework core with a metal-tannic acid (M-TA) coordination polymer shell (containing up to three different metal cations). Pyrolysis of these core-shell precursors affords hollow N-doped carbon capsules containing monometal sites (e.g., Fe-N_x, CoN_x, or Ni-N_x) or multimetal sites (Fe/Co-N_x, Fe/Ni-N_x, Co/Ni-N_x, or Fe/Co/Ni-N_x). This inventory allowed exploration of the relationship between catalyst composition and electrochemical activity for the oxygen reduction reaction (ORR) in acidic solution. H-Fe-N_x-C, H-Co-N_x-C, H-FeCo-N_x-C, H-FeNi-N_x-C, and H-FeCoNi-N_x-C were particularly efficient ORR catalysts in acidic solution. Furthermore, the H-Fe-N_x-C catalyst exhibited outstanding initial performance when applied as a cathode material in a proton exchange membrane fuel cell. The synthetic methodology introduced here thus provides a convenient route for developing next-generation catalysts based on earth-abundant components.

A 3-D nanoribbon-like Pt-free oxygen reduction reaction electrocatalyst derived from waste leather for anion exchange membrane fuel cells and zinc-air batteries

Fe-Nx and Fe-S-based ORR electrocatalysts have emerged as rightful candidates to replace Pt in fuel cells to make the technology cheap and sustainable. Fe-N-C catalysts are generally prepared by the pyrolysis of conducting polymers, metal-organic frameworks, aerogels, etc., and the combination of multiple heteroatoms and metal precursors. These precursors are mostly expensive and their synthesis involves multiple steps. In this report, we have demonstrated the synthesis of a Fe-N-C catalyst from the waste leather obtained from the footwear and other leather-consuming industries. The pyrolysis of leather with FeCl3 (metal source) results in the formation of a highly thin and porous nano-ribbon like morphology. Waste leather acts as a cost-free single source of heteroatoms like N, S and carbon. The catalyst synthesized at a temperature of 900 °C shows an overpotential of 40 mV and better durability compared to the commercial Pt/C catalyst. The catalyst is demonstrated as the cathode for alkaline exchange membrane fuel cell (AEMFC) and zinc-air battery (ZAB) applications. In the AEMFC, a power density of 50 mW cm-2 and an OCV of 0.92 V are obtained whereas, in the ZAB, it exhibited a power density of 174 mW cm-2 compared to 160 mW cm-2 of the system based on the Pt/C catalyst.

Iron-Nicarbazin derived platinum group metal-free electrocatalyst in scalable-size air-breathing cathodes for microbial fuel cells

In this work, a platinum group metal-free (PGM-free) catalyst based on iron as transitional metal and Nicarbazin (NCB) as low cost organic precursor was synthesized using Sacrificial Support Method (SSM). The catalyst was then incorporated into a large area air-breathing cathode fabricated by pressing with a large diameter pellet die. The electrochemical tests in abiotic conditions revealed that after a couple of weeks of successful operation, the electrode experienced drop in performances in reason of electrolyte leakage, which was not an issue with the smaller electrodes. A decrease in the hydrophobic properties over time and a consequent cathode flooding was suspected to be the cause. On the other side, in the present work, for the first time, it was demonstrated the proof of principle and provided initial guidance for manufacturing MFC electrodes with large geometric areas. The tests in MFCs showed a maximum power density of 1.85 W m^-2. The MFCs performances due to the addition of Fe-NCB were much higher compared to the iron-free material. A numerical model using Nernst-Monod and Butler-Volmer equations were used to predict the effect of electrolyte solution conductivity and distance anode-cathode on the overall MFC power output. Considering the existing conditions, the higher overall power predicted was 3.6 mW at 22.2 S m^-1 and at inter-electrode distance of 1 cm.

Pd supported on carbon containing nickel, nitrogen and sulfur for ethanol electrooxidation

Carbon material containing nickel, nitrogen and sulfur (Ni-NSC) has been synthesized using metal-organic frameworks (MOFs) as precursor by annealing treatment with a size from 200 to 300 nm. Pd nanoparticles supported on the Ni-NSC (Pd/Ni-NSC) are used as electrocatalysts for ethanol oxidation in alkaline media. Due to the synergistic effect between Pd and Ni, S, N, free OH radicals can form on the surface of Ni, N and S atoms at lower potentials, which react with CH₃CO intermediate species on the Pd surface to produce CH₃COO⁻ and release the active sites. On the other hand, the stronger binding force between Pd and co-doped N and S is responsible for enhancing dispersion and preventing agglomeration of the Pd nanoparticles. The Pd(20 wt%)/Ni-NSC shows better electrochemical performance of ethanol oxidation than the traditional commercial Pd(20 wt%)/C catalyst. Onset potential on the Pd(20 wt%)/Ni-NSC electrode is 36 mV more negative compared with that on the commercial Pd(20 wt%)/C electrode. The Pd(20 wt%)/Ni-NSC in this paper demonstrates to have excellent electrocatalytic properties and is considered as a promising catalyst in alkaline direct ethanol fuel cells.

A polyaniline-derived iron–nitrogen–carbon nanorod network anchored on graphene as a cost-effective air-cathode electrocatalyst for microbial fuel cells

A cost-effective Fe–N–C/G, which exhibited a distinct catalytic activity in neutral medium and air-cathode MFCs, was prepared for ORR catalyst.