Chloride Ion‐Specific Etching‐Driven Synthesis of Porous Cobalt‐Doped FeOOH Anodes for Robust Ni‐Fe Batteries

Why It Matters

The breakthrough lifts the energy density and cycle stability of low‑cost Ni‑Fe systems, positioning them as viable candidates for large‑scale, safe grid storage.

Key Takeaways

• Chloride ions enable rapid oxide layer dissolution
• Co-doping creates conductive pathways and abundant active sites
• Porous nanosheets deliver 1.4 mAh cm⁻², 94% efficiency
• Full Ni‑Fe cell reaches 0.9 mAh cm⁻² at 10 mA cm⁻²
• Strategy outperforms nitrate/sulfate etching, boosting aqueous battery performance

Pulse Analysis

Nickel‑iron batteries have long been praised for safety, low material cost, and a flat discharge curve, yet their market share has been limited by sluggish iron anode kinetics and modest areal capacities. Conventional iron electrodes suffer from dense oxide layers that impede electron transport and limit active site exposure, forcing designers to rely on expensive additives or complex architectures. As renewable integration demands affordable, long‑life storage, improving the intrinsic performance of the iron anode has become a critical research frontier.

The chloride‑ion‑specific etching method leverages the small hydrated radius and aggressive corrosivity of Cl⁻ to breach the passive FeOOH film, initiating a dissolution‑reconstruction cycle that yields a highly porous, cobalt‑enriched nanosheet network. Cobalt atoms substitute into the FeOOH lattice, enhancing electronic conductivity while preserving the hydroxide’s redox activity. This in‑situ growth on conductive Fe foam ensures intimate electrical contact, short diffusion paths, and a dramatically increased surface area—all without the need for binders or external templating agents.

Electrochemical testing shows the engineered anode delivering 1.4 mAh cm⁻² at 4 mA cm⁻² with 94 % coulombic efficiency after 1,000 cycles, and the assembled Ni‑Fe cell reaching 0.9 mAh cm⁻² at 10 mA cm⁻²—metrics that surpass many contemporary aqueous systems such as Zn‑based or Na‑ion batteries. By demonstrating a scalable, ion‑driven fabrication route, the study opens pathways for retrofitting existing iron infrastructure and accelerating the adoption of safe, low‑cost storage solutions in utility‑scale applications. Future work may explore alternative dopants or hybrid electrolytes to further push energy density while retaining the inherent robustness of the Ni‑Fe platform.