The Her/Oer Mechanistic Study Of An Feconi-Based Electrocatalyst For Alkaline Water Splitting

Herein, the electrodeposited-film electrode CFeCoNiP was fabricated to serve as a bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Kinetic Tafel slope analysis suggests that the HER follows the Volmer-Tafel mechanism (29 mV dec(-1)), indicating that the recombination of the two adsorbed hydrogen atoms is the rate-determining step. The FeCoNi-based thick film (thickness: 168.3 mu m) shows a metallic state favorable for electron transfer; on the other hand, in the case of the FeCoNi-based thin film (thickness: 389.2 nm), the in operando XAS investigation reveals that Fe3+-assisted water dissociation promotes the formation of Co2+-mu-H-Ni3+ (catalyst-H-ad) species, which subsequently undergoes reductive elimination to furnish H-2 gas via the HER process. During the OER, the CoNi-oxide matrix acts as a chemical and electroconductive host to build/stabilize the key intermediate [Fe4+& xe001;O/Fe3+-O & x2d9;] motifs; this subsequently triggers the catalytic O-O bond formation (30 mV dec(-1)) through the radical-radical coupling of the adjacent [Fe4+& xe001;O/Fe3+-O & x2d9;] motifs or/and OH- attack on the Fe4+-induced electrophilic oxygen center, leading to the release of O-2. The mechanistic experiments provide advanced insights into the catalytic kinetics/intermediates and demonstrate that the electronically cooperative interplay among Fe/Co/Ni leads to enhanced alkaline water electrolysis. The CFeCoNiP catalyst exhibits an excellent HER activity (specific activity j(s) = 0.227 mA cm(-2)) with a low charge transfer resistance (3.9 omega) and an overpotential of 37 mV, achieving the current density of 10 mA cm(2); moreover, it shows good OER activity (j(s) = 1.798 mA cm(-2)) with low charge transfer resistance (2.1 omega) and an overpotential of 250 mV, approaching a current density of 10 mA cm(-2) in a 1 M NaOH aqueous solution. The CFeCoNiP/NF (electrodeposited on Ni foam) electrode-pair device achieved the current densities of 100 and 500 mA cm(-2) at the voltages of 1.65 and 1.86 V, respectively, under alkaline conditions.