Electrochemical reduction of CO₂to HCOOH using zinc and cobalt oxide as electrocatalysts

Abstract

Present work studies the effect of synthesized Zinc (Zn) electrocatalyst towards reduction of CO 2 to products electrochemically (RCPE) using Cobalt oxide (Co 3 O 4 ) for water oxidation. Zn catalyst was prepared using electrodeposition method of zinc chloride dihydrate (ZnCl 2 .2H 2 O) solution. The synthesized electrocatalyst was characterized by XRD, FTIR and particle size analysis, which confirms the formation of Zn particles. Electrodes were prepared by depositing synthesized Zn and Co 3 O 4 on graphite plates and used as cathode and anode, respectively. The effects of applied voltage with time for RCPE were studied in carbonates and bicarbonates of sodium and potassium electrolytes. Ultra-fast liquid chromatography (UFLC) was used for the detection of end products from RCPE. However, HCOOH was the only product formed at all applied conditions. Maximum efficiencies were observed in bicarbonates than carbonates. In KHCO 3 electrolyte solution at 1.5 V, maximum Faradaic efficiencies of 78.54 % and 78.46 % for HCOOH were obtained at 5 and 10 min reaction. Similarly, in NaHCO 3 solution efficiencies of 60.5% and 64.7 % for 5 min and 10 min duration were obtained at 2.5 V. Ability of synthesized electrocatalyst towards RCPE was explained for all the applied conditions in detail.3 gases were emitted with CO 2 as major emission. This increases the CO 2 concentrations in atmosphere drastically from past few decades, which is the main cause for global warming effect. 1 In order to reduce these concentrations different techniques like photochemical 2 , electrochemical 3-6 , chemical 7 , biochemical 7 and radiochemical 7 were used and reported well.However, reduction of CO 2 electrochemically (RCPE) is considered as one of the promising methods for the elimination and conversion of atmospheric CO 2 to products. [8][9][10] Researchers are working on the RCPE for past few decades, mainly on electrocatalyst and its effect in different electrolytes. 3,11 Operating conditions and type of electrocatalyst plays a major role on the efficiency of RCPE and product selectivity. Electrocatalysts like Ag, Sn, and Au were used as electrodes for the reduction of CO 2 and various products including CO, HCOOH, H 2 and some liquid products were formed. 3 Electrolytes play a major role in RCPE, and their effects on reduction of CO 2 to carbon monoxide, oxalic acid, formic acid were reported. 12 Moreover, copper is accepted a suitable electrocatalyst in reducing CO 2 to hydrocarbons by several studies. 13 Ohya et al studied the effect of RCPE in methanol based electrolytes to evaluate the performance of copper oxides electrocatalyst. 14 Brito et al. reported the effect of photochemical reduction of CO 2 dissolved in carbonate electrolytes at Cu/Cu 2 O electrocatalyst and reported the formation of methanol and ethanol as products. 15 The reduction of CO 2 on copper electrode was studied and 16 different reaction products were reported. Out of these, methane and ethylene were identified with high efficiencies of current and remaining 14 pro...

Recent Trends, Benchmarking, and Challenges of Electrochemical Reduction of CO2 by Molecular Catalysts

“…Additionally, the integration of renewable energy systems (green electricity) into the grid can potentially create a carbon neutral energy cycle, and when driven by solar energy, offers a completely renewable energy cycle or negative carbon technology. [15,16] Therefore, recent research trends in electrocatalytic reduction of CO 2 have been shifting toward the development of molecular catalysts that can exist as either solutes in electrolytes or can be surface-confined on electrodes. [3][4][5][6][7] The recoverable energy density of the chemicals that can be converted from CO 2 is substantially higher than most battery technologies.…”

“…Converting CO 2 electrochemically into compounds with high energy densities, such as alcohols (methanol, ethanol), formates, and CO, represents a form of energy storage and is also adaptable to demand response or energy arbitrage technologies. [13,16] The tunable nature and electronic characteristics of molecular catalysts give access to a large variety of catalysts with high activity, selectivity, and durability, as well as their ability to be integrated into sophisticated nanoassemblies. [8][9][10][11] One of the greatest challenges of reducing CO 2 in an electrochemical cell is overcoming the immense energy barrier required to do so; the single electron reduction of CO 2 to CO 2 −˙, a common step in many CO 2 reduction mechanisms, requires an applied potential of −1.97 V measured versus standard hydrogen electrode (SHE).…”

“…[8][9][10][11] One of the greatest challenges of reducing CO 2 in an electrochemical cell is overcoming the immense energy barrier required to do so; the single electron reduction of CO 2 to CO 2 −˙, a common step in many CO 2 reduction mechanisms, requires an applied potential of −1.97 V measured versus standard hydrogen electrode (SHE). [15,16] Therefore, recent research trends in electrocatalytic reduction of CO 2 have been shifting toward the development of molecular catalysts that can exist as either solutes in electrolytes or can be surface-confined on electrodes. [12][13][14] However, despite the low potentials offered by catalytic electrodes, the cost of electrodes is not always viable when upscaled to industrial levels.…”

“…To alleviate this problem, many catalytic cathodes have been developed to avoid this intermediate and to reroute the reduction mechanism through alternate pathways requiring much lower applied potentials (a necessity if CO 2 electroreduction is to be implemented at industrial scale). [13,16] The tunable nature and electronic characteristics of molecular catalysts give access to a large variety of catalysts with high activity, selectivity, and durability, as well as their ability to be integrated into sophisticated nanoassemblies. [15,16] Therefore, recent research trends in electrocatalytic reduction of CO 2 have been shifting toward the development of molecular catalysts that can exist as either solutes in electrolytes or can be surface-confined on electrodes.…”

“…[12][13][14] However, despite the low potentials offered by catalytic electrodes, the cost of electrodes is not always viable when upscaled to industrial levels. [15,16] Therefore, recent research trends in electrocatalytic reduction of CO 2 have been shifting toward the development of molecular catalysts that can exist as either solutes in electrolytes or can be surface-confined on electrodes. [13,16] The tunable nature and electronic characteristics of molecular catalysts give access to a large variety of catalysts with high activity, selectivity, and durability, as well as their ability to be integrated into sophisticated nanoassemblies.…”