Laser synthesis of amorphous CoSx nanospheres for efficient hydrogen evolution and nitrogen reduction reactions

Abstract

Transition metal sulfides (TMSs) have been demonstrated to be excellent electrode materials for various applications of electrochemical energy conversion and storage. However, the synthesis of TMSs through conventional approaches commonly suffers from toxic or environmentally unfriendly reagents as well as time consuming procedures, high thermal power and energy loss. Herein, CoS_x nanospheres with uniform distribution and strong adhesion on carbon fiber cloths (CoS_x/CC-L) are synthesized via the confined laser temperature field under a H₂S atmosphere under normal temperature and pressure conditions. It is demonstrated that the high pressure field induced by a laser yields amorphous CoS_x containing numerous S vacancies, which could provide more active sites for enhancing the hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR). The as-prepared CoS_x/CC-L exhibits a low overpotential of ∼87 mV at 10 mA cm⁻² for the HER in 0.5 M H₂SO₄ aqueous electrolyte and maintains a stable catalytic performance for 15 h with a high current density of 650 mA cm⁻². In addition, a high ammonia (NH₃) production rate (12.2 μg h⁻¹ cm_cat⁻²) and Faraday efficiency (10.1%) of CoS_x/CC-L at −0.2 V vs. RHE in a neutral 0.05 M Na₂SO₄ electrolyte were obtained. The good proton activation and nitrogen adsorption abilities arising from the sulfur vacancies contribute to the active nitrogen association/hydrogenation process during the NRR. The laser synthesis provides an alternative process to produce efficient amorphous catalysts, which are expected to be promising HER and NRR electrocatalysts for energy conversion applications.