Developing low-cost, efficient, and stable trifunctional electrocatalyst for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is still a significant challenge. Herein, this study reports a zeolitic imidazolate framework (ZIF) derived trifunctional electrocatalyst, composed of Co 5.47 N and Co 7 Fe 3 (CoFeN) that embedded into 1D N-doped carbon nanotubes modified 3D cruciform carbon matrix (NCNTs//CCM). Benefiting from the robust interfacial conjugation of Co 5.47 N/Co 7 Fe 3 and the 1D/3D hierarchical structure with a large surface area, the as-prepared CoFeN-NCNTs//CCM display trifunctional electrocatalytic activity for ORR (half-wave potential of 0.84 V), OER (320 mV at 10 mA cm -2 ), and HER (−151 mV at 10 mA cm -2 ). The assembled Zn-air battery exhibits high power density (145 mW cm -2 ) , enhanced charge-discharge performance (voltage gap of 0.76 V at 10 mA cm -2 ), and long-term cycling stability (over 445 h). The resultant overall water-splitting cell achieves a current density of 10 mA cm -2 at 1.63 V, which can compete with the best reported trifunctional catalysts. What is more, the self-assembled Zn-air batteries are utilized to power the overall water splitting successfully, verifying great potential of the CoFeN-NCNTs//CCM as functional material for sustainable energy storage and conversion system.
Rational design of highly efficient, robust, and low-cost trifunctional electrocatalysts for oxygen reduction reaction (ORR), hydrazine oxidation reaction (HzOR), and hydrogen evolution reaction (HER) is extremely urgent for seawater-based renewable energy conversion and storage, including direct hydrazine fuel cells (DHzFC) and overall hydrazine splitting (OHzS). Herein, FeP/FeNi 2 P encapsulated in N, P co-doped hierarchical carbon (FeNiP-NPHC) in situ grown on nickel foam is fabricated via a hydrothermalpyrolysis-phosphidation procedure. Benefiting from the strong coupling effect among FeP, FeNi 2 P, and N, P co-doped carbon at the three-phase heterojunction interface, as well as the unique 1D/3D hierarchical structure, the as-prepared FeNiP-NPHC shows superior ORR (E 1/2 = 0.83 V), HzOR (E 100 = 7 mV), and HER (E 100 = -180 mV) performance in alkaline seawater. Density functional theory functions indicate that constructing three-phase heterojunction interface of FeNiP-NPHC can effectively adjust the d-band center and electronic structure, which is conductive to balance and optimize the trifunctional electrocatalytic performance. As proof of concept, the selfassembled DHzFC is utilized to power the OHzS in alkaline seawater successfully, verifying application potential of the FeNiP-NPHC as trifunctional electrocatalyst.
When compared with pure water, hydrogen produced by seawater electrolysis has a better practical application potential. By replacing the oxygen evolution reaction (OER) and competitive chlorine evolution reaction (ClER) with the thermodynamically favorable anodic hydrazine oxidation reaction (HzOR) in alkaline seawater, energy-saving hydrogen production can be achieved. In this study, Fe/Co dual-doped Ni 2 P and MIL-FeCoNi heterostructures (FeCo-Ni 2 P@MIL-FeCoNi) arrays with simultaneous cation doping and hetero-engineering provide excellent bifunctional electrocatalytic performance for HzOR and hydrogen evolution reaction (HER) in alkaline seawater electrolyte. Overall hydrazine splitting (OHzS) in seawater is impressive, with a low cell voltage of only 400 mV required to reach 1000 mA cm −2 and stable operation for 1000 h to maintain above 500 mA cm −2 . As a proof-of-concept, the OHzS system can save 3.03 kW h when producing 1.0 L of H 2 when compared with the N 2 H 4 -free seawater system, resulting in energy-saving H 2 production. Density functional theory calculations show that the combination of Co-doping and the fabrication of FeCo-Ni 2 P and MIL-FeCoNi heterointerfaces can result in a low water dissociation barrier, optimized hydrogen adsorption free energy toward HER, and favorable adsorbed dehydrogenation kinetics for HzOR. This processing route paves the way for a practical approach to the efficient utilization of hydrogen, which is abundant in the ocean energy field, to achieve a carbon-neutral hydrogen economy.
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