Temperature dependent electrocatalytic activity of molybdenum-based ZIF-67 nanorods for water splitting

Abstract

Several strategies have been adopted to enhance the electrochemical features of metal-organic framework structures for water splitting, however, a suitable conditions can effectively boost the electrocatalytic activity. Herein, molybdenum-based zeolite imidazolate frameworks (Mo2gZIF-67 and Mo4gZIF-67) have been synthesized by solvothermal process and electrocatalytic activity was examined at various elevating temperatures of 1 M KOH electrolyte. Mo4gZIF-67 nanorods showed the overpotential (η10) of 358 mV at 20 °C, which was improved to 221 mV at 80 °C for the oxygen evolution reaction. Mo4gZIF-67 nanorods exhibited the Tafel slope of 77 mV dec−1 at 80 °C and followed the Volmer-Heyrovsky mechanism. LSV curves reveal that Mo4gZIF-67 nanorods showed a greater current density and a good turnover frequency (TOF) of 221.0 ms−1 at the fixed VRHE of 0.7 V. Similarly, Mo4gZIF-67 nanorods revealed the η10 of 181 and 93 mV at 20 and 80 °C, respectively for the HER process. Mo4gZIF-67 nanorods displayed a Tafel slope of 95 mV dec−1 and TOF of 213.50 ms−1. The enhanced electrocatalytic activity may be due to rising temperatures, enhanced electrical conductivity at rising temperatures, well defined nanorods shape and greater ECSA, which provided the active sites and facile the flow of charge carriers for oxygen and hydrogen evolution reaction. The electrocatalyst, Mo4gZIF-67 nanorods exhibited a uniform current density during stability tests for 30 h at 20 °C, which was increased at 80 °C. Temperature elevation remarkably enhanced the HER and OER characteristics of the Mo4gZIF-67 nanorods and suggested an effective electrocatalyst for water splitting.