A lignin-derived N-doped carbon-supported iron-based nanocomposite as high-efficiency oxygen reduction reaction electrocatalyst

Fuel cells are a promising renewable energy technology that depend heavily on noble metal Pt-based catalysts, particularly for the oxygen reduction reaction (ORR). The discovery of new, efficient non-precious metal ORR catalysts is critical for the continued development of cost-effective, high-performance fuel cells. The synthesized carbon material showed excellent electrocatalytic activity for the ORR, with half-wave potential (E1/2) and limiting current density (JL) of 0.88 V and 5.10 mA·cm-2 in alkaline electrolyte, respectively. The material has a Tafel slope of (65 mV dec-1), which is close to commercial Pt/C catalysts (60 mV dec-1). Moreover, the prepared materials exhibited excellent performance when assembled as cathodes for zinc-air batteries. The power density reached 110.02 mW cm-2 and the theoretical specific capacity was 801.21 mAh g-1, which was higher than that of the Pt/C catalyst (751.19 mAh g-1). In this study, with the assistance of Mg5(CO3)4(OH)2·4H2O, we introduce an innovative approach to synthesize advanced carbon materials, achieving precise control over the material's structure and properties. This research bridges a crucial gap in material science, with potential applications in renewable energy technologies, particularly in enhancing catalysts for fuel cells.

Interfacial engineering of nickel selenide with CeO2 on N-doped carbon nanosheets for efficient methanol and urea electro-oxidation

The design of low cost, high efficiency electrocatalysts for methanol oxidation reactions (MOR) and urea oxidation reactions (UOR) is a pressing need to address the energy crisis and water pollution. In the present work, we developed Cerium dioxide (CeO2) and nickel selenide (Ni0.85Se) nanoparticles integrated into three-dimensional N-doped carbon nanosheets to be used as efficient and stable bifunctional electrocatalysts for MOR and UOR. By optimizing the selenization temperature, the CeO2-modified Ni0.85Se obtained at selenization temperature of 550 °C (CeO2-Ni0.85Se-550-NC) has the best MOR and UOR electrochemical performance. The CeO2-Ni0.85Se-550-NC potential only requires 1.309 V (MOR) and 1.294 V (UOR) to reach 10 mA cm-2, respectively. The DFT study reveals that CeO2-Ni0.85Se-550-NC has the best reaction path with the synergistic effect between CeO2 and Ni0.85Se. The outstanding catalytic performance of CeO2-Ni0.85Se-550-NC may be due to the cointeraction between CeO2 and Ni0.85Se, allowing more defects that function as catalytic sites while promoting fast electron transfer in the N-doped carbon substrate.

Effect of Cooperative Redox Property and Oxygen Vacancies on Bifunctional OER and HER Activities of Solvothermally Synthesized CeO2/CuO Composites

Herein, we report the synthesis of the CeO₂/CuO composite as a bifunctional oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrocatalyst in a basic medium. The electrocatalyst with an optimum 1:1 CeO₂/CuO shows low OER and HER overpotentials of 410 and 245 mV, respectively. The Tafel slopes of 60.2 and 108.4 mV/dec are measured for OER and HER, respectively. More importantly, the 1:1 CeO₂/CuO composite electrocatalyst requires only a 1.61 V cell voltage to split water to achieve 10 mA/cm² in a two-electrode cell. The role of oxygen vacancies and the cooperative redox activity at the interface of the CeO₂ and CuO phases is explained in the light of Raman and XPS studies, which play the determining factor for the enhanced bifunctional activity of the 1:1 CeO₂/CuO composite. This work provides guidance for the optimization and design of a low-cost alternative electrocatalyst to replace the expensive noble-metal-based electrocatalyst for overall water splitting.

Zinc- Fe/Fe5C2/Fe1-xS@Fe-N-C active sites grown on N-doped porous carbon toward efficient oxygen reduction reaction in zinc-air batteries

The development of efficient non-precious metal oxygen reduction reaction catalysts to replace Pt-based catalysts is of great significance to accelerate the commercial application of fuel cells. In this study, a hierarchical porous carbon oxygen reduction reaction catalyst with Fe/Fe₅C₂/Fe_1-xS@Fe-N-C active sites was developed via a simple and efficient solid-phase synthesis method. The introduction of zinc inhibited the growth and agglomeration of the nanoparticles and induced the formation of active nitrogen species and porosity, thus boosting the catalytic activity. The optimal FeZn-N-C-1 catalyst exhibited a high half-wave potential of 0.846 V, which is 24 mV higher than that of the commercial Pt/C, with a 4-e^- reaction path under alkaline conditions. When the FeZn-N-C-1 catalyst is employed as a cathode in a zinc-air battery, it achieves a high open circuit voltage of 1.54 V, power density of 143.6 mW cm^-2 and specific capacity of 804 mA h g^-1.

Enhancement of microwave absorption performance of porous carbon induced by Ce (CO3) OH

In recent years, electromagnetic pollution has become more and more serious, resulting in a very negative impact on people's health. Therefore, it is important to develop efficient microwave absorbers to reduce electromagnetic pollution. Here, we construct a novel absorbing material of the polymer gel-derived porous carbon decorated by rare earth compounds (Ce (CO₃) OH). When the thickness is 2.2 mm, the composite exhibits excellent microwave absorption performance with the optimal RL_min value and EAB reached up to -47.67 dB and 5.52 GHz, respectively, covering the Ku band. The high-efficiency microwave absorption is mainly attributed to the synergistic effect of dipole polarization, defect polarization and interfacial polarization. This work not only provides a new view for designing superior absorber materials, but also lay a foundation for their real applications.

Revealing the Real Role of Etching during Controlled Assembly of Nanocrystals Applied to Electrochemical Reduction of CO2

In recent years, the use of inexpensive and efficient catalysts for the electrocatalytic CO₂ reduction reaction (CO₂RR) to regulate syngas ratios has become a hot research topic. Here, a series of nitrogen-doped iron carbide catalysts loaded onto reduced graphene oxide (N-Fe₃C/rGO-H) were prepared by pyrolysis of iron oleate, etching, and nitrogen-doped carbonization. The main products of the N-Fe₃C/rGO-H electrocatalytic reduction of CO₂ are CO and H₂, when tested in a 0.5 M KHCO₃ electrolyte at room temperature and pressure. In the prepared catalysts, the high selectivity (the Faraday efficiency of CO was 40.8%, at −0.3 V), and the total current density reaches ~29.1 mA/cm² at −1.0 V as demonstrated when the mass ratio of Fe₃O₄ NPs to rGO was equal to 100, the nitrogen doping temperature was 800 °C and the ratio of syngas during the reduction process was controlled by the applied potential (−0.2~−1.0 V) in the range of 1 to 20. This study provides an opportunity to develop nonprecious metals for the electrocatalytic CO₂ reduction reaction preparation of synthesis and gas provides a good reference

Controlled assembly of nitrogen-doped iron carbide nanoparticles on reduced graphene oxide for electrochemical reduction of carbon dioxide to syngas

The electrocatalytic CO₂ reduction reaction (CO₂RR) decreases the amount of greenhouse gas in the atmosphere while enabling a closed carbon cycle. Herein, iron oleate was used as a precursor to produce oleic acid-coated triiron tetraoxide nanoparticles (Fe₃O₄@OA NPs) by pyrolysis, which was then assembled with reduced graphene oxide (rGO) and doped with dicyandiamide as a nitrogen source to obtain nitrogen-doped iron carbide nanoparticles assembled on rGO (N-Fe₃C/rGO NPs). The catalyst prepared by nitrogen doping at 800 °C with an Fe₃O₄@OA NPs to rGO weight ratio of 20:1 showed good activity and stability for the CO₂RR. At -0.3 to -0.4 V, the H₂/CO ratio of the product from the catalyzed CO₂RR was close to 2; thus, the product can be used for Fischer-Tropsch synthesis. The results of a series of experiments and X-ray photoelectron spectroscopy analysis showed that the synergy between the CN and FeN groups in the catalyst can promote the reduction of CO₂ to CO. This work demonstrates a facile method for improving the catalytic reduction of CO₂.

Recent advances on preparation and environmental applications of MOF-derived carbons in catalysis

Carbon materials derived from metal organic frameworks (MOFs) have excellent properties of high surface area, high porosity, adjustable pore size, high conductivity and stability, and their applications in catalysis have become a rapidly expanding research field. In this review, we have summarized the synthesis strategies of MOF-derived carbons with different physical and chemical properties, obtained through direct carbonization, co-pyrolysis and post-treatment. The potential applications of derived carbons, especially monometal-, bimetal-, nonmetal-doped and metal-free carbons in organo-catalysis, photocatalysis and electrocatalysis are analyzed in detail from the environmental perspective. In addition, the improvement of catalytic efficiency is also considered from the aspects of increasing active sites, enhancing the activity of reactants and promoting free electron transfer. The function and synergy of various species of the composites in the catalytic reaction are summarized. The reaction paths and mechanisms are analyzed, and research ideas or trends are proposed for further development.

Novel Heteroatom-Doped Fe/N/C Electrocatalysts With Superior Activities for Oxygen Reduction Reaction in Both Acid and Alkaline Solutions

The exploration of noble metal-free catalysts with efficient electrochemical performance toward oxygen reduction reaction in the acid electrolyte is very important for the development of fuel cells technology. Novel pyrolyzed heteroatom-doped Fe/N/C catalysts have been regarded as the most efficient electrocatalytic materials for ORR due to their tunable electronic structure, and distinctive chemical and physical properties. Herein, nitrogen- and sulfur-doped (Fe/N/C and Fe/N/C-S) electrocatalysts were synthesized using ferric chloride hexahydrate as the Fe precursor, N-rich polymer as N precursor, and Ketjen Black EC-600 (KJ600) as the carbon supports. Among these electrocatalysts, the as prepared S and N-doped Fe/N/C-S reveals the paramount ORR activity with a positive half-wave potential value (E _1/2) 0.82 at 0.80 V vs. RHE in 0.1 mol/L H₂SO₄ solution, which is comparable to the commercial Pt/C (Pt 20 wt%) electrocatalyst. The mass activity of the Fe/N/C-S catalyst can reach 45% (12.7 A g^-1 at 0.8 V) and 70% (5.3 A g^-1 at 0.95 V) of the Pt/C electrocatalyst in acidic and alkaline solutions. As result, ORR activity of PGM-free electrocatalysts measured by the rotating-ring disk electrode method increases in the following order: Fe/N/C<Fe/N/C-S, in both basic and acidic medium. This scientific work offers a facile approach to design and synthesizes efficient heteroatom-doped catalytic materials for electrochemical reactions in energy devices.