Fabrication of Nanoporous Nickel–Iron Hydroxylphosphate Composite as Bifunctional and Reversible Catalyst for Highly Efficient Intermittent Water Splitting

Abstract

Global-scale application of water-splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources has called for the development of oxygen- and hydrogen-evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Here, we report the controlled electrodeposition of porous nickel-iron hydroxylphosphate (NiFe-OH-PO) nanobelts onto the surface of macroporous nickel foams (NF) as a bifunctional electrocatalyst for efficient whole-cell water electrolysis. The NiFe-OH-PO/NF electrode shows both high water oxidation and water reduction catalytic activity in alkaline solutions and is able to deliver current densities of 20 and 800 mA cm at overpotentials of merely 249 and 326 mV for oxygen-evolution reaction, current densities of 20 and 300 mA cm at overpotentials of only 135 and 208 mV for hydrogen-evolution reaction. Further, in a two-electrode water electrolytic cell, the bifunctional NiFe-OH-PO/NF electrodes can obtain the current densities of 20 and 100 mA cm at an overall cell potential of only 1.68 and 1.91 V, respectively. Remarkably, the NiFe-OH-PO/NF catalyst also represents prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation.

Ultrathin Amorphous Iron–Nickel Boride Nanosheets for Highly Efficient Electrocatalytic Oxygen Production

“…On the contrary,b are Ni foam showedi nsignificanta ctivity in the OER. [41] For more such comparable materials, see Ta bles S2 and S3 in the Supporting Information. [41] For more such comparable materials, see Ta bles S2 and S3 in the Supporting Information.…”

Ultralow FeIII Ion Doping Triggered Generation of Ni3S2 Ultrathin Nanosheet for Enhanced Oxygen Evolution Reaction

“…Electrochemical water splitting for H 2 and O 2 production could enable the large‐scale storage of intermittent energy from the sun, wind, or other renewable sources, thus reducing the use of conventional fossil fuels and alleviating the impact of climate change . As one of the two half‐cell reactions in water electrolysis,, oxygen evolution reaction (OER) is a sluggish process as it involves a four electrons reaction process .…”

Reversible ternary nickel‐cobalt‐iron catalysts for intermittent water electrolysis

“…This is ascribed to the oxidation of absorbed hydrogen generated during HER at the NiCoFe/NF electrode, as when the absorbed hydrogen gas from HER is removed by exposing the electrode into air, the current stair is no longer detected in the subsequent anodic current (Figure S18). This could be attributed to the hydrogen storage capacity of the Ni and/or Co‐based alloys, which is usually beneficial to the corrosion resistance properties of the electrode during shutdowns . Intriguingly, the NiCoFe/NF catalysts exhibit distinctly different color when used for OER (black) and HER (silver grey), as shown in Figure S14, attributed to transformation of the transition metal components in the electrode to different oxidation states, for example, from transparent Ni 2+ to black Ni 3+ .…”

“…Furthermore, for practical applications, the OER and HER catalysts need not only to have prolonged stability, but also to withstand frequent power interruptions during cell shutdowns. It is known that during power interruptions (ie, when no power is provided by renewable energy sources), a reverse current takes place in water electrolyzer from anode to cathode through bipolar plate, and degrades the electrodes by the reduction of the anode and/or oxidation of the cathode, resulting in compositional as well as structural change and eventually catalyst deactivation . This is particularly important for storage of electricity generated from renewable resources such as solar and wind because these energy sources are intermittent and power interruptions are almost inevitable.…”