A strategy for easy synthesis of carbon supported Co@Pt core–shell configuration as highly active catalyst for oxygen reduction reaction

An oxygen-mediated galvanic battery reaction strategy has been developed to one-step synthesize carbon-supported Co@Pt core–shell nanostructures. Relying on this strategy, a structural evolution of 3-D Pt-on-Co bimetallic nanodendrites into Co@Pt core–shell configuration is readily achieved in our study. These well-supported and low-Pt-content nanostructures show superior electrocatalytic activities to oxygen reduction reaction. Especially, the supported Co@Pt core–shell electrocatalyst for oxygen reduction reaction shows a high activity with the maximal Pt-mass activity of 465 mA mg⁻¹ Pt at 0.9 V (vs. RHE). The present investigation clearly demonstrates that the design and synthesis of the core–shell nanostructures is a viable route for building Pt-based electrocatalysts with optimized utilization efficiency and higher cost performance.     

One-step synthesis of oxygen incorporated V–MoS2 supported on partially sulfurized nickel foam as a highly active catalyst for hydrogen evolution

Highly active noble-metal-free catalysts for hydrogen evolution reaction (HER) are essential for the sustainable production of hydrogen. MoS₂ based HER catalysts are potentially competitive to noble metals but facing the challenges of low conductivity, density of active sites and intrinsic activity in basal planes. Herein, oxygen incorporated V–MoS₂ supported on partially sulfurized nickel foam (V–Mo(x)S/NF) are synthesized as binder-free HER catalysts via a one-step in-situ hydrothermal method. By controlling the fed atomic ratios of V/Mo, the optimal V–Mo(0.05)S/NF shows the low HER overpotential of ~31 and ~115 at 10 mA cm⁻² and 100 mA cm⁻², respectively in alkaline electrolyte, which is among the most active noble-metal and noble-metal-free HER catalysts reported. In V–Mo(0.05)S/NF, the introduced V and partially sulfurized nickel foam increases the conductivity. The hedgehog-like morphology ensures the exposure of high-density active sites. More importantly, the incorporated surface oxygen can be readily tuned by the fed atomic ratios of V/Mo, which plays the primary role in promoting the intrinsic HER activity for V–Mo(x)S/NF. This work demonstrates the feasibility of boosting HER through the precise control of incorporated surface oxygen in MoS₂ based catalysts.     

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.     

Cobalt–Iron nanoparticles encapsulated in mesoporous carbon nanosheets: A one-pot synthesis of highly stable electrocatalysts for overall water splitting

Advancement of cost-effective, highly efficient and non-noble metal-based bifunctional electrocatalysts is considered an attractive approach to overcome the energy defect and environmental pollution challenges. Herein, this study presents a simple one-pot approach to synthesize cobalt-Iron nanoparticles encapsulated in mesoporous carbon nanosheets (Co₃Fe₇@CNSs) by the pyrolysis method. The Co₃Fe₇@CNSs-750/4h electrocatalyst exhibits a notable performance, low overpotential of 181 and 301 mV at a current density of 10 mA cm^?2 and small Tafel slope of 124.8 and 38.59 mV dec^?1, large active surface area 18.20 and 21.18 mF cm^?2, and low charge transfer resistance 4.92 and 9.42 Ω for hydrogen and oxygen evolution reactions, respectively, in 1.0 M KOH. Overall water splitting, with the set-up of two-electrode cells acquires the 10 mA cm^?2 of current density at 1.610 V in 1.0 M KOH. The combined structure of cobalt-iron nanoparticles encapsulated in carbon nanosheets; it could enhance the surface area and, provide more active sites that improve the overall catalytic activity. Not only this but also the synergistic effect due to different temperature treatments which significantly influenced the structural formation. However, the major involvement of this study is concerned with the production of economical non-noble metal-based electrocatalysts at an industrial scale for renewable energy to sustainability.     

Ultrasonic-assisted synthesis of highly active catalyst Au/MnOx–CeO2 used for the preferential oxidation of CO in H2-rich stream

A series of nano-gold catalysts supported on binary oxides MO_x–CeO₂ (atomic ratio M/Ce = 1:1, M = Mn, Fe, Co, Ni) are prepared by deposition–precipitation (DP). An innovative and rather convenient ultrasonic pretreatment of the support is employed for Au/MnO_x–CeO₂ preparation. It is found that for preferential CO oxidation Au/MnO_x–CeO₂ is more active than Au/CeO₂. Ultrasonic pretreatment of MnO_x–CeO₂ further promotes the performance of Au/MnO_x–CeO₂, with CO conversion increased by 24 % at 120 °C. Meanwhile, the selectivity of oxygen to CO₂ is promoted in the whole temperature range, especially in 80–120 °C, the selectivity is increased by 15–21%. HR-TEM and XRD results indicate that ultrasonic pretreatment is favorable to the formation of much smaller gold nanoparticles (<5 nm). The characterization of XPS, UV–vis DRS, H₂-TPR and CO-TPR confirms that the strong interaction between Au and the support effectively inhibits the dissociation and oxidation of H₂ over the ultrasonically pretreated catalyst Au/MnO_x–CeO₂, making it highly selective to CO oxidation.     

Facile synthesis of supported Pt–Cu nanoparticles with surface enriched Pt as highly active cathode catalyst for proton exchange membrane fuel cells

Carbon supported Pt–Cu catalyst (PtCu/C) with surface enriched Pt was synthesized by annealing the Pt-deposited Cu particles. X-ray diffraction (XRD) results indicate the formation of disordered Pt–Cu alloy phase with a high level of Cu/Pt atomic ratio. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) analysis confirm the surface enrichment of Pt. Electrochemical measurements show that PtCu/C has 3.7 times higher Pt mass activity toward the oxygen reduction reaction (ORR) than commercial Pt/C. The enhanced ORR activity of PtCu/C is attributed to the modified electronic properties of surface Pt atoms, which reduces the surface blocking of the ORR oxygenated species.     

Ru–Ni/GA-MMO composites as highly active catalysts for CO selective methanation in H2-rich gases

CO selective methanation (CO-SMET) is as an ideal H₂-rich gases purification measurement for proton exchange membrane fuel cell system. Herein, the graphene aerogel-mixed metal oxide (GA-MMO) supported Ru–Ni bimetallic catalysts are exploited for CO-SMET in H₂-rich gases. The results reveal that a three-dimensional network structure GA-MMO aerogel with higher specific surface area, better thermal stability and more defects or structural disorders is formed when MMO:GO mass ratio is in the range of 1–4. After loading of Ru, more NiO are reduced to metallic Ni by hydrogen spillover effect, and thus obviously enhances the reactivity. The GA-MMO supported Ru–Ni catalyst exhibits more excellent metal dispersion, reducibility, stronger CO adsorption and activation than the MMO supported Ru–Ni catalyst, thereby resulting in better catalytic performance and stability. This work offers new insights into the construction of highly active catalyst for the efficient generation of high-quality H₂ from H₂-rich gases.     

Solid-state synthesis method for the preparation of cobalt doped Ni–Al2O3 mesoporous catalysts for CO2 methanation

In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al₂O₃ catalysts with various Co loadings, and the prepared catalysts were used in CO₂ methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al₂O₃ sample with a specific surface area of 129.96 m²/g possessed the highest catalytic performance in CO₂ methanation (76.2% CO₂ conversion and 96.39% CH₄ selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.     

In-situ synthesis of hollow Co–MoS2 nanocomposites on the carbon nanowire arrays/carbon cloth as high-performance catalyst for hydrogen evolution reaction

The design and synthesis of non-precious metal catalysts that effectively convert water into molecular hydrogen in an acidic environment is essential to reduce the energy loss in the water splitting process. Among them, molybdenum disulfide (MoS₂) is considered as an effective alternative to Pt-based materials due to its excellent structure properties. Here, by using metal-organic framework (MOF) as the precursor, sodium molybdate as molybdenum sources and thiourea as sulfur sources, a hollow structure of Co–MoS₂ electrocatalyst was prepared on highly conductive carbon nanowire arrays/carbon cloth (CA/CC) by hydrothermal reaction. The combination of carbon nanowire arrays and carbon cloth ensures the high conductivity, while the hollow Co–MoS₂ structure promotes the penetration of electrolytes and the release of hydrogen bubbles. The overpotential is only 296 mV when the current density was ~1500 mA/cm², which shows excellent catalytic hydrogen evolution activity of the material. In addition, the three-dimensional hollow structure avoids the use of adhesives between the active material and the self-supporting material, which can improve the stability of the material and provides a new idea to design commercial electrocatalysts.     

Hetero-structure CdS–CuFe2O4 as an efficient visible light active photocatalyst for photoelectrochemical reduction of CO2 to methanol

In the present paper, hetero-structured CdS–CuFe₂O₄ nanocomposite was synthesized by a facial method to convert CO₂ to methanol in the photoelectrochemical (PEC) system. The synthesized catalysts were characterised by XRD, Raman spectroscopy, TEM, FESEM, EDX, XPS, UV–vis and PL spectroscopy. The CdS–CuFe₂O₄ photocatalyst showed ~6 times higher photocurrent compared to the CuFe₂O₄ at −0.35 V vs. NHE of bias potential under CO₂ environment as revealed by chronoamperometry results. Incident photon to current efficiency (IPCE) for CuFe₂O₄ and CdS–CuFe₂O₄ at 470 nm were found as 7.28 and 12.09%, respectively which clearly indicates the proficiency of CdS–CuFe₂O₄ heterojunction to absorb the visible light resulting in e⁻/h⁺ generation and the charge transfer during PEC CO₂ reduction. Products in aqueous and gas phases were analysed which confirmed the selective production of methanol with trace amounts of H₂ and CO. The CdS–CuFe₂O₄ catalyst demonstrated 72% and 16.9% of Faradaic and quantum efficiencies, respectively in terms of methanol production where a methanol yield of 23.80 μmole/Lcm² was achieved in CO₂ saturated aqueous solution of NaHCO₃ (0.1 M). Detailed investigation revealed that the conduction band (CB) of the CdS in the heterojunction catalyst could act as a CO₂ reduction site by trapping photogenerated electrons from the highly photosensitive CuFe₂O₄ while the water oxidation could take place at the valance band (VB) of CuFe₂O₄.     

Synthesis of Cr2O3–Al2O3 powders with various Cr2O3/Al2O3 molar ratios and their applications as support for the preparation of nickel catalysts in CO2 methanation reaction

The Methanation of CO₂ to CH₄ is a significant route to save energy and reduce CO₂ emission. In this work, a series of Cr₂O₃–Al₂O₃ powders were synthesized by a novel and simple solid-state method and considered as the carrier for the nickel catalysts in CO₂ methanation. The BET area and pore volume of the supports decreased with the decrease in Al₂O₃/Cr₂O₃ molar ratio. The results indicated that the increase in Cr₂O₃ content improved the catalytic performance and 15 wt%Ni/Cr₂O₃ catalyst exhibited the highest CO₂ conversion of 80.51%, and 100% CH₄ selectivity at 350 °C. The results indicated that the CO₂ conversion improved with the increment in H₂/CO₂ molar ratio from 2 to 5. The improvement in CO₂ conversion was also observed with decreasing GHSV due to the longer residence time of the reactants on the catalyst surface. Also, the results showed that increasing calcination temperature led to a decrease in CO₂ conversion. The 15 wt%Ni/Cr₂O₃ catalyst exhibited high stability in carbon dioxide methanation reaction.     

Controlled synthesis of Mn3O4/Co9S8–Ni3S2 on nickel foam as efficient electrocatalyst for oxygen evolution reaction

Advances in electrochemical interfaces have greatly facilitated the development of new energy systems that can replace traditional fossil fuels. Oxygen evolution reaction (OER) is the core reaction in the new energy conversion system to produce hydrogen. Here, nanorods structure of Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 was designed and assembled. The Mn₃O₄ has served as an appropriate matrix to build a composite structure with Co₉S₈–Ni₃S₂ to enhance the stability of catalyst. And the introduction of Mn regulated the electronic structure of Ni and Co, which increased the OER activity of matericals. Further characterization and electrochemical testing have suggested that between polymetallic can effectively optimize conductivity and enhance reaction kinetics. Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 can achieve overpotential of 188 mV at the current density of 10 mA cm^?2 in alkaline solution, with small Tafel slope of 43.2 mV dec^?1 and satisfactory stability of 30 h at 10 mA cm^?2. This work may show a feasible reference in the design of high-efficient OER catalysts.