A Hybrid of the Fe4N-Fe Heterojunction Supported on N-Doped Carbon Nanobelts and Ketjen Black Carbon as a Robust High-Performance Electrocatalyst.

Herein, an extremely simple l-alanine-assisted pyrolysis method was proposed for the construction of a novel hierarchically porous hybrid of Fe4N-Fe supported on N-doped carbon nanobelts and Ketjen black carbon (denoted as Fe4N-Fe@N-C/N-KB). It has been found that the participation of l-alanine in pyrolysis can dramatically increase the total pyridinic-N/graphitic-N content in Fe4N-Fe@N-C/N-KB, which is peculiarly conducive to the enhancement of ORR performance. The in-site formation of the Fe4N-Fe heterojunction via the thermal reduction and decomposition of Fe3N as well as the introduction of cheap KB can significantly improve the ORR performance. As a result, the activity, durability, and methanol tolerance of this hybrid are comprehensively better than those of commercial 20 wt % Pt/C, promising future applications in practical devices. Density functional theory calculations disclose that the highly improved ORR activity of Fe4N-Fe@N-C/N-KB also benefits from the favorable electron penetration and excellent electronic conductivity between the Fe4N nanoparticles and the N-incorporated carbon frameworks.

Self-Supported Hierarchical IrO2@NiO Nanoflake Arrays as an Efficient and Durable Catalyst for Electrochemical Oxygen Evolution.

Although traditional IrO2 nanoparticles loaded on a carbon support (IrO2@C) have been taken as a benchmark catalyst for the oxygen evolution reaction (OER), their catalytic efficiency, operation stability, and IrO2 utilization are far from satisfactory due to the inferior powdery structure and inevitable corrosion of both IrO2 and C under the oxidizing potentials. Here, a rational design of a self-supported hierarchical nanocomposite, composed of IrO2@NiO nanoparticle-built porous nanoflake arrays vertically growing on nickel foam, is proposed, which is demonstrated as a versatile strategy to achieve improved OER activity, remarkable long-term stability, and significantly reduced loading of IrO2 (0.62 atom %). Impressively, the resultant catalyst drives a steady OER current density of 10 mA cm-2, requiring 278 mV overpotential in 1.0 M KOH electrolyte for 25 h and outmaneuvring commercial IrO2@C with much higher mass loading. Further electrochemical investigation and mechanism analysis disclose that the greatly improved electrocatalytic activity stems from the advantageous hierarchical structure and the synergistic effect between IrO2 and underlying potential-induced NiOOH, whereas the outstanding durability is attributed to the unique role of NiO in preventing IrO2 dissolution.