Interface-Engineered NiSe/Ni₃Se₂ Catalysts on Nickel Foam for Efficient Cr(VI) Reduction via Formic Acid Activation

We engineered a NiSe/Ni₃Se₂ heterostructure on nickel foam that activates formic acid for rapid hexavalent chromium detoxification. We used one-step hydrothermal growth and probed structure and mechanism by diffraction and spectroscopy, electron microscopy, electron paramagnetic resonance with 5,5-dimethyl-1-pyrroline N-oxide, and batch and fixed-bed tests. The optimized catalyst removed 99.7% of 50   mg   L⁻¹ hexavalent chromium in 40   minutes at 25 °C, achieved full removal of 1   mg   L⁻¹ in 20   minutes, tolerated common ions, and maintained 100% removal for 180   h in continuous flow. Mechanistic analyses show a radical pathway dominated by hydrogen radicals (H ⁎ ) and carbon dioxide radical anions ( C O 2 • − ), promoted by selenium vacancies and tightly coupled nickel selenide interfaces that accelerate formic-acid activation and interfacial charge transfer. Operating without external energy input, this monolithic architecture avoids powder recovery and minimizes pressure drop and cost, offering a general route to defect-engineered selenides for efficient, low-cost environmental redox remediation.