# Electrochemical Deposition of Copper on Epitaxial Graphene
## 1 Introduction  
Copper (Cu) deposition is one of the key processes in the electronic industry for circuit interconnections, increasingly replacing aluminum [1]. The electrodeposition of copper has the advantages over physical and chemical vapor deposition methods since it seems to be cheapest and best method to fill vias and trenches. Moreover, copper is one of the most-investigated metal catalysts, stipulating studies of electrodeposition on a variety of carbon materials, especially graphite [2; 3; 4]. The electronic conductivity of graphite is established due to the planar conjugation of the \(sp^{2}\) bonds in a single graphene sheet as a primary building block of all graphitic materials. This defines a significant anisotropy of the density of states (DOS) for in-plane and out-of-plane (edge and basal planes, correspondingly) electronic conduction, which is the origin of the duality in the general properties of all graphitic materials [5; 6]. The use of macroscale defect-free graphene sheets [7] allows for the avoidance of contributions from the reactive edge plane of high DOS. In the past decade, huge efforts have been made to conceptualize graphene-copper material hybridization for practical applications [8; 9; 10; 11; 12; 13]. Particularly, it was discovered that the addition of graphene to the copper matrix can improve the mechanical and electrical properties of Cu, causing a significant increase in the electrical conductivity, Young's modulus, shear modulus, and Vickers hardness as well as a reduction in the thermal expansion coefficient [8; 9; 10; 11]. The aforementioned advantages create excellent prerequisites for copper-graphene (Cu-Gr) composites to be used as reliable interconnection materials, electrical contact materials forultrahigh-voltage circuit breakers and printed electronics. The enhanced conductivity of the Cu-Gr composite also determines its exploitation as a high-performance counter electrode in solar cells [12; 13]. Furthermore, due to the larger heat transfer coefficient and higher corrosion resistance of Cu-Gr hybrids in 3.5% NaCl medium when compared to pure copper [14; 15; 16; 17; 18], these materials are very promising for engineering applications (for instance, anti-corrosion coatings) in sea water and for heat transfer applications, respectively. Copper-graphene nanohybrids were, however, recognized and appreciated mainly for their role in the development of efficient catalytic and ultrasensitive detection technologies. The benefits gained from the interaction between graphene-based materials and copper have been used for reduction of 4-nitropend (4-NP) to 4-aminophenol [19; 20], oxidation of hydrazine [21; 22], electro-oxidation of methanol [23], hydrogen evolution reaction (HER) [24; 25], the electrochemical reduction of CO\({}_{2}\) to ethanol [26], oxidative carbonylation of methanol [27], CO\({}_{2}\) cycloaddition to propylene oxide (PO) [28], formic acid synthesis by CO\({}_{2}\) hydrogenation [29] and CO\({}_{2}\) electroreduction for methane and methanol production [30]. Beyond the issue of high-performance catalysts, it is worth mentioning that Cu-Gr composites have also been applied to the electrochemical detection of ascorbic acid and dopamine [31], organophosphorus pesticide [32], heavy metals [33; 34], glucose [35; 36; 37; 38; 39], chlorophenol pollutants in wastewater [40], hydroquinone and catechol [41], nitrite [42; 43], nitrogen dioxide (NO\({}_{2}\)) [44] and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) [45]. Numerous density functional theory (DFT) calculations shed light on the adsorption of different gases (H\({}_{2}\)S [46; 47], CO [48], CO\({}_{2}\) [49], N\({}_{2}\)O [50], H\({}_{2}\)[51; 52; 53]) and organic molecules [54; 55; 56] onto Cu-decorated/doped/anchored graphene, thereby providing the solid theoretical background that is required to design efficient sensing devices. Until now we have been giving an overview of most relevant applications of copper-graphene composite materials.