An organic–inorganic heterojunction electrocatalyst for highly efficient urea oxidation

Abstract

Constructing a p–n heterojunction allows the modulation of the interfacial electronic structure and boosts electron transfer, leading to enhanced electrocatalytic performance. Herein, an organic–inorganic heterojunction electrocatalyst made of Ni(OH)₂, a triazine-based covalent organic framework (COF), and multi-walled carbon nanotubes (CNTs), denoted as Ni(OH)₂/COF/CNT, is reported to exhibit significantly enhanced electrocatalytic performance for urea oxidation in comparison with its single- and double-component counterparts (Ni(OH)₂, COF/CNT, Ni(OH)₂/CNT, and Ni(OH)₂/COF). As revealed by its band structure analysis, the constructed Ni(OH)₂-COF (p–n) heterojunction enables a built-in electric field to boost charge transfer across the heterointerface (from the inorganic Ni(OH)₂ to the organic COF), resulting in significantly improved catalytic activity. The mass activity is 363 A g_Ni(OH)2⁻¹ at 1.5 V (vs. reversible hydrogen electrode, RHE) for the Ni(OH)₂/COF/CNT heterojunction electrocatalyst, showing 322 and 72% enhancement in comparison with Ni(OH)₂ and Ni(OH)₂/CNT, respectively. Moreover, Ni(OH)₂/COF/CNT exhibits a considerable turnover frequency (TOF, 0.11 s⁻¹ at 1.5 V), large reaction rate constant (k = 1.9 × 10⁶ cm³ mol⁻¹ s⁻¹), high coulombic efficiency (∼98%), and meritorious catalytic stability (24 hours at 20 mA cm⁻²) for urea oxidation. The present work enriches the design strategies for developing advanced electrocatalysts.