Electrochemical synthesis of NiCo layered double hydroxides on nickel-coated graphite for water splitting: understanding the electrochemical experimental parameters

Abstract

The electrochemical synthesis of nickel-cobalt (Ni-Co) layered double hydroxides (LDHs) on a nickel-coated graphite support for water splitting applications was investigated. Three different electrochemical approaches, namely, cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP), were employed for evaluating the electrodeposition of Ni-Co LDHs. The graphite support was initially coated with a thin layer of Ni by applying 50 mA cm^-2 constant current density for 120 s. Raman spectroscopy results confirmed the intercalation of nitrates, evidenced by the characteristic Raman bands at 1033 cm^-1 (<i>ν</i> ₁) and 1329 cm^-1 (<i>ν</i> ₃). These characteristic bands were indicative of nitrate intercalation, a key feature of LDHs, further supporting the classification of the synthesized material as NiCo LDHs on a nickel-coated graphite support. It was observed that the electrochemical routes used for the synthesis influenced the morphology, composition, and electrochemical behavior of the obtained Ni-Co LDHs. Moreover, atomic force microscopy (AFM) measurements revealed distinct nanoscale surface characteristics associated with the synthesis methods, with the Ni-Co LDH synthesized <i>via</i> the CV route exhibiting higher surface heterogeneity than that synthesized <i>via</i> the constant potential method (CA), resulting in a more textured surface. These findings were further supported by roughness average (Ra) values, where CV-synthesized Ni-Co LDH displayed the highest <i>R</i> _a of 221 nm, indicating a more extensive active surface area. The electrochemical performance, both for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), were correlated with these surface variations. This study provides valuable insights into the electrochemical experimental parameters for the synthesis of Ni-Co LDHs and their potential application in water splitting processes.