**Abstract**

In the last decade, there is some research on the conversion of CO2 to energy form. CO2 can be converted to value-added chemicals including HCOOH, CO, CH4, C2H4, and liquid hydrocarbons that can be used in various industries. Among the methods, electrochemical methods are of concern regarding their capability to operate with an acceptable reaction rate and great efficiency at room temperature and can be easily coupled with renewable energy sources. Besides, electrochemical cell devices have been manufactured in a variety of sizes, from portable to large-scale applications. Catalysts that optionally reduce CO2 at low potential are required. Therefore, choosing a suitable electrocatalyst is very important. This chapter focused on the electrochemical reduction of CO2 by Zn-Ni bimetallic electrocatalyst. The Zn-Ni coatings were deposited on the low-carbon steel substrate. Electrochemical deposition parameters such as temperature in terms of LPR corrosion rate, microstructure, microcracks, and its composition have been investigated. Then, the electrocatalyst stability and activity, as well as gas intensity and selectivity, were inspected by SEM/EDX analysis, GC, and electrochemical tests. Among the electrocatalysts for CO2 reduction reaction, the Zn65%-Ni35% electrode with cluster-like microstructure had the best performance for CO2 reduction reaction according to minimum coke formation (<10%) and optimum CO and H2 faradaic efficiencies (CO FE% = 55% and H2 FE% = 45%).

**Keywords:** electrocatalyst, electrochemical method, CO2 reduction reaction, Zn-Ni, energy conversion, pollution, catalyst activity and stability

## **1. Introduction**

Carbon dioxide is a chemical compound made up of one carbon atom and two oxygen atoms. It is existing in minimal concentrations in the atmosphere and behaves as a greenhouse gas that promotes environmental warming and pollution. However, carbon dioxide can be used as a source of high-value chemicals, as a source of sustainable energy. So far, many activities have been done to convert CO2 into chemical materials, which can be applied as fuel for the industries.

With the increasing demand for energy and population growth, CO2 emissions have grown as a by-product of power and industrial plants. In the last decade, CO2 conversion has increased to other beneficial products. This process is useful for reducing pollution and warming of the earth. Developing a variety of electrocatalysts with high efficiency and good stability is a crucial issue [1].

The electrochemical CO2 reaction reduction in recent decades has become crucial because it is a good reaction to artificial fuels and energy storage. When this process is linked to renewable energy sources such as solar cells, it can be a good alternative to fossil fuels. It also reduces CO2 emissions in the atmosphere. But there are major problems for the reaction of CO2 reduction, which includes low efficiency and low catalytic activity with cost-effective catalysts. Therefore, there is an important challenge in the present research, so that catalyst with better selectivity and higher activity and stability can be developed [2].

In recent years, several studies were done on various electrocatalysts, but yet, there are problems in Faradaic Efficiency (FE), Current Density (CD), Energy Efficiency, electrocatalyst deactivate, the internal resistance of electrocatalysts, and the potential for scalability to the large sizes without the loss of efficiency, because CO2 is a thermodynamically stable molecule, it is fully oxidized [3–12]. A suitable electrocatalyst to reduce CO2 is necessary to reach a low-cost process with acceptable selectivity and efficiency. In recent decades, the electrochemical reduction of CO2 has interested a lot of consideration as low-cost electricity can come from renewable sources of energy such as solar and wind [13–18].

#### **1.1 Zn-Ni coating**

Zinc as another choice of cadmium has been studied for its ability to resist corrosion regarding its sacrificial properties and has demonstrated its ability to provide adequate corrosion behavior results through the study conducted on mechanical properties and corrosion protection of Zn electrodeposition [19]. Though Zn is considered a possible option, its corrosion behavior does not look acceptable in an aggressive condition with greater temperatures. Electrodeposited Zn coatings study tests indicated that pure Zn has weak corrosion resistance properties compared to cadmium [20]. Therefore, the need for metal coatings with corrosion properties outstanding to those of pure Zn and comparable or improved to cadmium has driven the industrial production of electrodeposits involving Zn alloys with VIIIBgroup metals (e.g. Zn-Fe, Zn-Ni, Zn-Co) [21]. The electrodeposition of Zn and its eight-group metals including Co, Fe, and Ni have been extensively investigated and analyzed for their ability to be an excellent corrosion resistant alloy.

#### *1.1.1 Zinc-nickel alloy corrosion behavior*

In recent years, a lot of research has been performed to investigate the possibility that the Zn-Ni alloy could be a substitute with a corrosion property corresponding to the toxic coatings of cadmium. Much research has also been done to distinguish and determine the corrosion resistance of the Zn-Ni coatings [22–25]. The corrosion resistance of deposited Zn-Ni coatings on steel substrate indicated as having the acceptable corrosion property (corrosion rate: ~ 11 mm/year) was reached for Zn-Ni alloys in the range from 12 to 15 wt.% of Ni content in the coating so that the coating with Ni content from 12 to 15 wt.% maintains the anodic behavior of the steel, retaining the sacrificial behavior with a decrease corrosion rate after the addition of Ni, which increases the potential nearer to the substrate providing protection for a too time [21]. This has been endorsed by reports conducted by other authors [22–25] who have stated that Zn-Ni coating with a Ni amount of 12 to 15 wt.% supplies

*Investigation of Zn/Ni-Based Electrocatalysts for Electrochemical Conversion of CO2 to SYNGAS DOI: http://dx.doi.org/10.5772/intechopen.95626*

adequate corrosion protection. While the coating retains its sacrificial behavior regarding the steel substrate, whenever the alloy with more than 30 wt.% of Ni turns nobler than the substrate, missing its sacrificial behavior. Hence, it led to preferential corrosion of the steel, and Ni amount of less than 10 wt.% in the coating produced smaller barrier performance. Byk et al. [25] performed tests showing the greatest corrosion resistance properties utilizing a poor acid chloride solution with the Zn-(15 wt.%) Ni coating having the least corrosion CD, demonstrating the best corrosion protection, and this is qualified to the existence of the γ phase (Ni5Zn21) which is gained with Zn-Ni coatings with Ni amount from 12 to 15 wt.% [25]. The coatings of Zn-Ni coating with 10–15 wt.% of Ni have more suitable corrosion resistance, better weldability, and superior formability. The presence of Ni in the Zn-Ni alloy in the optimal range from 12 to 15 wt.% reduces the rate of Zn dissolution, supplying greater and longer corrosion resistance than pure Zn [24].
