(286c) Nife Alloy Nanotube Arrays As Highly Efficient Bifunctional Electrocatalysts for Overall Water Splitting at High Current Densities

Renewable energy driven electrolytic water splitting is regarded as the most promising way to supply clean hydrogen fuel to answer the present and future energy and environmental issues. For electrolytic water splitting, electricity consumption is the major operation cost, accounting for more than 50%. Therefore, developing high efficiency water splitting electrocatalysts for both anode and cathode to reduce the working cell voltages is most critical for reduction of the production cost. One-dimensional nanostructure arrays have found applications in a wide range of areas, including electrical devices, biological sensors, photoelectrocatalytic electrodes, magnetic recording media, etc. Nevertheless, they have rarely been applied in electrolytic water splitting. Notably, 1-D nanostructure arrays provide not only high surface-to-volume ratio for enlarged reaction surface areas but also aligned 1-D nanostructure, suitable for guided electron transport. Furthermore, for electrolytic water splitting applications, the un-entangled 1-D nanostructure array, for example nanotube arrays, provides proper inter-tube space for fast mass transfer of the electrolyte and escape of the generated gas bubbles. Here, a bubble-releasing assisted pulse electrodeposition method was developed to create metallic alloy, NiFe, nanotube arrays in one-step. The NiFe alloy nanotube array exhibited excellent bifunctional electrolytic activities, achieving low overpotentials of 100 mV for the hydrogen evolution reaction and 236 mV for the oxygen evolution reaction at 10 mA cm^–2, both in 1M KOH at room temperature. For overall water splitting, the NiFe alloy nanotube array delivered 10 mA cm^–2 at an ultralow cell voltage of 1.58 V, among the top tier of the state–of–the–art bifunctional electrocatalysts. The NiFe alloy nanotube array also exhibited ultrastability at high current densities, experiencing only a minor chronoamperometric decay of 6.5% after a 24 hr operation at 400 mA cm^–2. The nanotube array structure proves to be a promising new architecture design for electrocatalysts.