Coupling of Bifunctional CoMn-Layered Double Hydroxide@Graphitic C3 N4 Nanohybrids towards Efficient Photoelectrochemical Overall Water Splitting.

The development of durable, low-cost, and efficient photo-/electrolysis for the oxygen and hydrogen evolution reactions (OER and HER) is important to fulfill increasing energy requirements. Herein, highly efficient and active photo-/electrochemical catalysts, that is, CoMn-LDH@g-C3 N4 hybrids, have been synthesized successfully through a facile in situ co-precipitation method at room temperature. The CoMn-LDH@g-C3 N4 composite exhibits an obvious OER electrocatalytic performance with a current density of 40 mA cm-2 at an overpotential of 350 mV for water oxidation, which is 2.5 times higher than pure CoMn-LDH nanosheets. For HER, CoMn-LDH@g-C3 N4 (η50 =-448 mV) requires a potential close to Pt/C (η50 =-416 mV) to reach a current density of 50 mA cm2 . Furthermore, under visible-light irradiation, the photocurrent density of the CoMn-LDH@g-C3 N4 composite is 0.227 mA cm-2 , which is 2.1 and 3.8 time higher than pristine CoMn-LDH (0.108 mA cm-2 ) and g-C3 N4 (0.061 mA cm-2 ), respectively. The CoMn-LDH@g-C3 N4 composite delivers a current density of 10 mA cm-2 at 1.56 V and 100 mA cm-2 at 1.82 V for the overall water-splitting reaction. Therefore, this work establishes the first example of pure CoMn-LDH and CoMn-LDH@g-C3 N4 hybrids as electrochemical and photoelectrochemical water-splitting systems for both OER and HER, which may open a pathway to develop and explore other LDH and g-C3 N4 nanosheets as efficient catalysts for renewable energy applications.