Chemical Engineering

The deposition of praseodymium oxide (PrO2) films on diamond electrodes is of interest for electrochemical applications, because of the catalytic and permselective properties of this material. In this work, PrO2 was deposited on commercial boron-doped diamond (BDD) electrodes from solutions of praseodymium nitrate in hydrogen peroxide, where a local increase of pH at the electrode surface is used to precipitate hydrated praseodymium oxide at the solution-electrode interface. For particular deposition conditions, it is observed that pronounced lateral heterogeneities are seen in the observed deposition rate, arising from lateral fluctuations in the electrochemical activity of the diamond electrodes used. It is also observed that the use of scanning electrochemical techniques enables oxide deposition with good spatial control to be achieved.

MnO2 nanoparticles (NPs) with 1.8 ± 0.2 nm in diameter were successfully produced using an ethylene glycol-assisted synthesis with successive hydrolysis and condensation reactions. The tiny NPs were used as precursors for producing three-dimensionally ordered macroporous (3DOM) electrodes using a colloidal crystal-templating method. The specific capacitances of 3DOM MnO2 electrodes depend on their pore diameters. The 3DOM electrode with about 200-nm pore diameter provides 3.0-, 2.0-, and1.3-fold higher specific capacitance than the dense film and the 3DOM electrodes with larger pores, 400 nm and 900 nm, respectively. The ultrahigh specific capacitance of the 200-nm 3DOM electrode is 765 F g− 1 measured in 0.5 M Na2SO4 at the scan rate of 2 mV s− 1. In addition, the capacity retention of the 200-nm 3DOM electrode is over 98% of the original capacitance after 2000 cycles while that of the dense film is only 78%.► We report a facile synthesis of 1.8 ± 0.2-nm MnO2 nanoparticles. ► MnO2 nanoparticles used as precursors for producing highly-ordered porous pseudocapacitors. ► Porous pseudocapacitors exhibit ultrahigh capacitance (765 F/g) due to faster ion transportation. ► Pseudocapacitive behavior of the porous pseudocapacitors depends on their pore sizes. ► Smaller pore diameter provides higher specific capacitance.

Although supercapacitors have higher power density than batteries, they are still limited by low energy density and low capacity retention. Here we report a high-performance supercapacitor electrode of manganese oxide/reduced graphene oxide nanocomposite coated on flexible carbon fiber paper (MnO2–rGO/CFP). MnO2–rGO nanocomposite was produced using a colloidal mixing of rGO nanosheets and 1.8 ± 0.2 nm MnO2 nanoparticles. MnO2–rGO nanocomposite was coated on CFP using a spray-coating technique. MnO2–rGO/CFP exhibited ultrahigh specific capacitance and stability. The specific capacitance of MnO2–rGO/CFP determined by a galvanostatic charge–discharge method at 0.1 A g−1 is about 393 F g−1, which is 1.6-, 2.2-, 2.5-, and 7.4-fold higher than those of MnO2–GO/CFP, MnO2/CFP, rGO/CFP, and GO/CFP, respectively. The capacity retention of MnO2–rGO/CFP is over 98.5% of the original capacitance after 2000 cycles. This electrode has comparatively 6%, 11%, 13%, and 18% higher stability than MnO2–GO/CFP, MnO2/CFP, rGO/CFP, and GO/CFP, respectively. It is believed that the ultrahigh performance of MnO2–rGO/CFP is possibly due to high conductivity of rGO, high active surface area of tiny MnO2, and high porosity between each MnO2–rGO nanosheet coated on porous CFP. An as-fabricated all-solid-state prototype MnO2–rGO/CFP supercapacitor (2 × 14 cm) can spin up a 3 V motor for about 6 min.

Abstract Deoxygenation of pyrolysis vapor from palm fruit cake by different catalysts was prior investigated by using Ni/γ-Al2O3, Mo/γ-Al2O3, and NiMo/γ-Al2O3 prepared by wet impregnation method. NiMo/γ-Al2O3 showing the highest degree of deoxygenation (%DOD) activity was subsequently mixed with metal oxides: CeO2, TiO2, and ZrO2. Effects of the catalysts on upgrading of pyrolysis vapor from palm fruit cake at 450°C under N2 atmosphere in a semi-batch process were investigated. The oil products were analyzed for CHNO elements by elemental analyzer, chemical compositions by a gas chromatograph coupled to a mass spectrometer (GC-MS), and higher heating values (HHV) by Dulong's equation. Catalysts have been characterized and discussed related to the product yields and properties. Acidity and acid strength of the catalyst mixture play an important role on the products. NiMo/γ-Al2O3 improved properties of the crude bio-oil by increasing organic phase yield, %DOD, and HHV. Addition of CeO2 to NiMo/γ-Al2O3 reduced phenol compound in the liquid products while addition of TiO2 to NiMo/γ-Al2O3 provided high aromatics and hydrocarbons comparable to those obtained from NiMo/γ-Al2O3/ZrO2. Addition of ZrO2 to NiMo/γ-Al2O3 exhibited the highest organic phase yield (%), %DOD (71%), and HHV (37 MJ/kg).