Electrochemical deposition (ECD) has been a primary method of metal plating for a variety of applications for nearly 100 years. Its popularity is due to its straightforward design, low cost, uniform results, and successful application to a wide range of metals and substrates. Many factors have been shown to influence the composition, texture, and chemical properties of the resultant deposit, such as the current density, the nature and concentration of metal ions, the solution temperature and composition, the applied current waveform, the substrate surface, and agitation. In particular, additives play a complex role in metal deposition due to their ability to greatly alter the growth mechanism and resultant deposit structure. There exists a vast body of work related to the role of additives in various plating solutions, however the majority of investigations on additive effects are focused on planar deposition. For instance, boric acid is a common additive found in nearly all aqueous transition metal plating solutions, yet its influence on metal nanostructure deposition has not been well studied.

  In this work, we focus on the impact of additives on the growth of metal nanostructures.  Specifically, we investigate the role of boric acid in the ECD of nickel nanotubes (NTs) and nanowires (NWs).  First, we demonstrate the difference in the growth mechanism and nanostructure morphology in the presence and absence of boric acid with electron microscopy and electrochemical analyses.  The ECD conditions are modified to further probe the role of boric acid in the 1D growth of nickel nanostructures.  The results confirm the function of boric acid in the surface-directed growth of nickel nanostructures.  Second, we employ the boric acid-controlled growth mechanism in the synthesis of advanced nickel nanostructures.  The potential for the role of boric acid to be applied to the deposition of additional metals is realized through the synthesis of nickel alloy NTs and NWs.  Additionally, the advantage of the boric acid-controlled surface-directed growth mechanism is demonstrated through the straightforward synthesis of segmented nanostructures and a 3D interconnected nanotube network.