High Performance Core/Shell Ni/Ni(OH)₂ Electrospun Nanofiber Anodes for Decoupled Water Splitting

Abstract

Decoupled water splitting is a promising new path for renewable hydrogen production, offering many potential advantages such as stable operation under partial-load conditions, high-pressure hydrogen production, overall system robustness, and higher safety levels. Here, the performance of electrospun core/shell nickel/nickel hydroxide anodes is demonstrated in an electrochemical-thermally activated chemical decoupled water splitting process. The high surface area of the hierarchical porous electrode structure improves the utilization efficiency, charge capacity, and current density of the redox anode while maintaining high process efficiency. The anodes reach average current densities as high as 113 mA cm −2 at a working potential of 1.48 V RHE and 64 mA cm −2 at 1.43 V RHE , with a Faradaic efficiency of nearly 100% and no H 2 /O 2 intermixing in a membrane-free cell.

Systematic Engineering on Ni‐Based Nanocatalysts Effectively Promote Hydrogen Evolution Reaction

“…[15][16][17] However, it is pity that the intrinsic catalytic activity of Ni-based materials are difficult to compare with Pt/C because of the relatively strong Gibbs free energy of adsorbed H* (ΔG H *) as well as lack of water decomposition sites and usually have poor long-term durability, which limits the commercial application of Ni-based materials. [18][19][20][21] Therefore, designing a Ni-based electrocatalyst with high stability and intrinsic activity can be compared with Pt/C is a major challenge at present.For the preparation method, researchers have explored many means to synthesize nanomaterial electrocatalysts in past decades, such as hydrothermal reaction, [22] solvothermal method, [23] electrodeposition and high temperature calcination method, [24][25][26] and so on. Unfortunately, these means and nanocatalysts have some shortcomings.…”

Metal nanoparticles entrapped in metal matrices

“…Last but not least, in order to further demonstrate the generality of the approach to other porous surface area metallic supports, another type of Ni doped with palladium was prepared, using this time electrospun Ni fibers, about 250 nm in diameter and 1 micron long, synthesized by hydrogen reduction from NiO mats (provided generously by the authors of ref. 40 ). On these Ni fibers, Pd was in situ grown to form Pd-grown@Ni-fiber (similar to type C), according to: Ni (s) + Pd (aq) 2+ ⇒ Pd (s) + Ni (aq) 2+ .…”

Across the Board: Gabriele Centi on Decoupling Electrocatalytic Reactions to Electrify Chemical Production

“…A versatile solid‐state redox couple is Ni(OH) 2 /NiOOH. These materials, originally developed for rechargeable alkaline batteries, have been used for electrochemical–thermally‐activated chemical (E‐TAC) water splitting [18–20] . The interesting concept in E‐TAC is that the nickel hydroxide anode is charged (oxidized) to nickel oxyhydroxide (NiOOH), without concurrent oxygen evolution, at room temperature (25 °C).…”

“…These materials, originally developed for rechargeable alkaline batteries, have been used for electrochemical–thermally‐activated chemical (E‐TAC) water splitting. [ 18 , 19 , 20 ] The interesting concept in E‐TAC is that the nickel hydroxide anode is charged (oxidized) to nickel oxyhydroxide (NiOOH), without concurrent oxygen evolution, at room temperature (25 °C). This stage is followed by a thermally activated chemical stage in which the cold alkaline electrolyte is replaced by a hot (95 °C) alkaline electrolyte to promote a spontaneous chemical reaction between the charged NiOOH anode and water that reduces the anode back to Ni(OH) 2 while evolving oxygen (Figure 1 ).…”

“…Doping with cobalt [18] or traces of iridium [21] shifts the oxidation cathodic potential by several tens of mV. The use of electrospun core–shell nickel/nickel hydroxide anodes [19] and carbon‐cloth‐supported nickel hydroxide [20] in the form of a nanoflake microstructure allows to improve mass transport and overall performance, besides stability. A further effort is necessary, however, to improve the behavior because both current density (≈10 mA cm −2 ) and capacity (the anode can be charged for ≈200 s) are still low, compared to redox mediators in liquid phase and, in general, to the need of achieving a spatiotemporal decoupling as that indicated above.…”