P-NiFe2O4/N-Doped Carbon Nanotubes/NiFe Multi-Phase Heterojunctions for Overall Water Splitting and Urea Electrolysis

Graphical P-doped NiFe 2 O 4 nanoparticles/N-doped carbon nanotubes are prepared via a hydrothermal method followed by phosphorization. The CNTs greatly enhance the electron transfer rate and the P-doping effectively modulates the charge distribution around Ni and Fe atoms, optimizes the energy barriers of adsorption of intermediates, urea and water dissociation, thereby accelerating the kinetics of water splitting and urea electrolysis. The design and construction of highly efficient electrocatalysts for overall water splitting and urea electrolysis are significantly important for promoting energy conversion and realizing green hydrogen production. In this work, we constructed a multi-phase heterojunction through a simple hydrothermal and phosphorization process. The P-doped NiFe 2 O 4 (P-NiFe 2 O 4 ) nanoparticles were uniformly anchored on the bamboo-like N-doped carbon nanotubes (NCNTs) grown via a NiFe-alloy autocatalysis. The electronic structure and coordination environment of active species were optimized by the synergistic action of P doping, well-dispersed ultrafine NiFe 2 O 4 , and NCNTs matrix with good conductivity, enhancing their quantity and activity for electrocatalysis. Consequently, the P-NiFe 2 O 4 /NCNTs/NiFe exhibits excellent HER and OER activities with an overpotential of 111 and 266 mV at 10 mA cm −2 in 1 M KOH, respectively. The symmetrical overall water-splitting cell using P-NiFe 2 O 4 /NCNTs/NiFe as both anode and cathode delivers 10 mA cm −2 at a voltage of 1.604 V in 1 M KOH. Notably, the two-electrode cell requires a low voltage of 1.467 V to achieve a current density of 10 mA cm − 2 in 1 M KOH solution with 0.6 M urea. This designed catalysts display outstanding reaction kinetics and catalytic stability. This work provides useful guidance for applying transition metal-based catalysts for hydrogen production.