Mixed-valent cobalt phosphate/borophene nanohybrids for efficient electrocatalytic oxygen evolution reaction.

Developing efficient, low-cost, non-precious and stable electrocatalyst is necessary for sustainable electrocatalytic water splitting. Recently, borophene has emerged as a novel two-dimensional material with exciting properties. Although several researchers have theoretically predicted its applicability towards effective electrocatalytic water splitting, studies on its practical applications are still limited. In this regard, a mixed-valent cobalt phosphate/borophene nanohybrid (BCoPi) was synthesized using hydrothermal method, and its activity towards oxygen evolution reaction (OER) was systematically studied. The electron-deficient nature of borophene enables activation of catalytic sites and facilitates electron transport owing to its highly conductive nature. It can act as a proton acceptor along with phosphate groups, as well as provide multiple secondary active sites in addition to Co, breaking the scaling relation of OER. For BCoPi, achieving a current density of 50 mA cm-2, 100 mA cm-2 and 500 mA cm-2 requires an overpotential of 337 mV, 357 mV and 401 mV, respectively, in an alkaline medium, that are superior to pristine cobalt phosphate (CoPi). It also exhibits low Tafel slope of 61.81 mV dec-1, suggesting faster OER kinetics and excellent long-term stability. This study will extend the development and application of borophene-based heterostructures for highly active and stable electrocatalysts for various applications.

Graphene oxide wrapped Mix-valent cobalt phosphate hollow nanotubes as oxygen evolution catalyst with low overpotential.

Development of an efficient, stable and inexpensive catalyst for oxygen evolution reaction (OER) is critical to electrochemical water splitting. In this regard, a precious-metal free electrocatalyst has been synthesized employing a hydrothermal route. The prepared graphene oxide wrapped cobalt phosphate nanotubes deposited on Ni foam electrode shows a low overpotential of 234 mV at a current density of 10 mA/cm2 for OER in 1(M) KOH, lower than a benchmarking electrocatalyst IrO2 at the same current density. The performance figures clearly defy the volcano limitations. The mixed-valency induced delocalization of charge satisfies Sabatier Principle for ideal catalysts and graphene oxide ensures improved charge transfer. Moreover, the designed electrocatalyst performs efficiently even on prolonged use under mass transfer limitation conditions.