Electrochemical Preparation of Hydrogen Bronze Films For Reduction of Carbon Dioxide to Formate
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ElectrochemicalPreparation of Hydrogen Bronze Films For Reduction of Carbon Dioxideto Formate
Carbondioxide (CO2)is one of the compounds that are used in a lot of chemical reactions.It has many important uses in life. Carbon dioxide gas is effectivein extinguishing fires. It can also be used to remove caffeine fromcoffee plant through analytical methods1.The compound can also be used in laboratories to produce usefulproducts via electrochemical, photochemical and analytical methods.The electrochemical method opens up new options of converting CO2to a myriad of products. Carbon dioxide can also be convertedelectrochemically to methane,methanol, ethanol, ethylenecarbonmonoxide, formic acid, formaldehyde, and propanol.The electrochemical method of converting CO2intoother products is so far the best method since it is a short and easyprocedure. An electro-fuel is an example of a liquid fuel that isproduced from compounds such as CO2and H2Oby the electrochemicalmethod. Sometimes, catalysts are incorporated in the electrochemicalprocess to increase the speed of interactions.
Thephotochemical reduction of carbon dioxide plays a major role indealing with challenges that result from continued use of fossilfuel. Photochemical reduction of CO2using ruthenium, tris-phenanthroline as the chromophore and pyridineadjusted to a pH of 5.0 results mainly in formation of formate andmethanol. Visible light irradiation at 470 ± 20 nm can be used asthe CO2reduction catalyst. This reaction is conducted without using anymetals since metals often catalyze the reaction and convert carbondioxide to others products. Hydrocarbonscan be producedwith less selectivity in a photochemical method however, there aredifferent ways through which the selectivity for hydrocarbonscan be improved3.
ConvertingCO2to Ethanol by the Electrochemical Method
Theprocess of converting CO2to ethanol using the electrochemical method has been researched fordecades. There are many metals that help to convert carbon dioxide tohydrocarbonssuch as copper, platinum, iron, tin, silver and gold.Copper (Cu) is the best metal catalyst in the electrochemicalconversion method because it is capable of electrochemicallyconverting carbon dioxide into more than 30 different chemicals.Copper reacts with saturated aqueous solutions in the presence ofcarbon dioxide and produces a mixture of compounds. This reaction isdominated either by water (H2O)or by hydrocarbons. When Copper is supported by grapheme, catalyticactivity is enhanced in the reaction because Copper is stronger. Theprocess stabilizes the interaction with carbon dioxide and developsselectivity into hydrocarbons such as methanol and methane. The nextstep is the most important one since it results in the production ofethanol. Theinteraction between Copper (Cu) and Carbon nanospike (CNS) controlsreduction to alcohol by the electrochemical method. It is followed bya reaction between adjacent catalytic sites on CNS and copper (Cu),and the nanostructured morphology results in a high yield of ethanol.Carbon nanospike (CNS) with copper nanoparticles (Cu/CNS) have ahigher selectivity for CO2with a high efficiency to produce ethanol4.
ElectrochemicalConversion of Carbon Dioxide to Formate
Itis the first pathway to produce Formate by using polymer electrolytemembrane cells.Theexperiment happens between two catalyzed electrodes. The cell acts asa source of carbon dioxide, water, and power.The cathodegets organic products from electroreduction of carbon dioxide and theanode gets oxygen from the water.
Figure3: Polymer electrolyte membrane cell
Thiskind of cell helps carbon dioxide conversion to happen at highefficiencies. Formate is formed at high efficiency. However, theefficiency of formate is dependent on the concentrations of carbondioxide at the surface of the electrodes. Low concentrations ofcarbon dioxide lead to low efficiency that results in low productionof formate. CO2cannow be converted to Formate by the electrochemical method.
MolybdenumOxide Film Electrodes
Usinga thin film of transition metal oxide because thin film is compatiblewith electrochemical devices can do electrochemical conversion of CO2to Formate. The electrodeposition technique is a good way to make athin film on a large surface. During the first step of the reaction,anelectric cell containing two electrodes is used. Then, the platinumelectrode is used to show the results while the glass slides thathave been coated with Indium Tin Oxide (ITO) are used to evaluate thethickness of the electrodeposits. The ITO electrodes together withthe insulating tape and cyclic voltammetry are useful for thedeposition process. Next, each film is placed in a beaker that hasHSO4to get the cyclic voltammetric responses. The cyclic voltammogramsare used to determine the resultant link between the anode and howthick the measured ﬁlms on the ITO are. A Sulphuric acid solutionis then used to determine the deposit on the glassy carbon. Beforethe electrochemical experiments, the electrolyte solutions remove theoxygen by a 10-minute flow of nitrogen gas. The nitrogen gas shouldcontrol the atmosphere of solutions during the experiment. Theexperiment happens at a temperature of 298 K.
Preparationof MoO3 Thin Film
Beforebeginning the process of ﬁlm deposition, the GC electrode needs tobe cleaned twice in distilled water for 5 min. The working electrodehas to be in an equilibrium state before each impedance measurementis done. A modification of the MoO3 thin ﬁlm is then carried out.The molybdenum oxide ﬁlm functions well under cyclic voltammetricstates. Its color and thickness also change. ThePH of the solution is important when determining thickness and colorof the ﬁlms and a thinner film can be obtained in less acidicsolutions.
Fig.1: Shows the cyclic voltammograms obtained in the process ofdeposition of the ﬁlm.
Cyclicvoltammetry is used to characterize deposition of the film. Thevoltammograms of the films associated with molybdenum oxide arerecorded with 5mM sulphuric acid from 0.165 to 20.65 voltages atpotential rates that range between 0.1 and 5 mV/s.
Fig.2: Shows effects of the rate of the cyclic voltammetric results onthe GC containing the molybdenum oxide ﬁlm within 5 mM of H2SO4and Fig.3: Shows the rate range that it applies by cathodic peak
Theresistance is found through increasing the hydrogen content of thefilm. When hydrogen atoms come into the film, the color changes. Byusing an electrochemical deposition, the molybdenum oxide ﬁlm ismade.6
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