Innovative Ir-Doped NiFe2O4/TiO2 anode for sustainable hydrogen production and advanced wastewater treatment

In the realm of environmental engineering and material science, Professor Kangwoo Cho's team at POSTECH has made notable progress in advancing decentralized saline wastewater treatment and hydrogen production. By focusing on scalable heterojunction anodes, their research addresses critical challenges in achieving efficient pollutant removal and resource recovery in sustainable water management systems. The centerpiece of their work is an Ir-doped NiFe₂O₄ (NFI) anode integrated with a TiO₂ overlayer, which combines exceptional catalytic performance, selectivity, and stability for multifunctional applications.

The NFI/TiO₂ anode was synthesized using a straightforward drop-casting and thermal annealing process, enabling the production of scalable and uniform electrodes. Electrochemical analyses, including cyclic voltammetry, impedance spectroscopy, and operando X-ray absorption spectroscopy, revealed that the TiO₂ overlayer plays a dual role. It not only protects the underlying NiFe₂O₄ structure but also enhances catalytic activity by facilitating effective Cl⁻ chemisorption and electron transfer. The optimized design demonstrates remarkable efficiency in the chlorine evolution reaction (ClER), achieving superior activity and selectivity compared to conventional materials such as IrO₂.

Performance evaluations under laboratory conditions validated the dual functionality of the NFI/TiO₂ anode. During galvanostatic wastewater electrolysis, the anode achieved nearly stoichiometric ammonium-to-nitrogen conversion with minimal formation of undesired byproducts such as nitrites or nitrates. At the same time, the hydrogen evolution reaction (HER) was maintained at high efficiency, with current efficiencies exceeding 85%. This simultaneous pollutant degradation and hydrogen production highlight the potential of the anode for energy recovery in wastewater treatment.

To demonstrate real-world applicability, the research team implemented the NFI/TiO₂ anode in a pilot-scale water electrolysis cell with a capacity of 10 liters. The system treated simulated toilet wastewater, achieving complete ammonium removal and significant reductions in chemical oxygen demand (COD) and turbidity. Operando fluorescence spectroscopy and chemical analyses further confirmed the effective breakdown of dissolved organic matter and the absence of secondary pollutants. These findings underscore the potential of the NFI/TiO₂ anode for decentralized water treatment in diverse settings, including remote and resource-constrained areas.

Beyond wastewater treatment, the material design and performance insights from this research extend to other fields. The integration of Ir-doped spinel structures with protective TiO₂ layers opens new avenues for catalytic applications in environmental remediation, energy storage, and chemical synthesis. The team's innovative approach to optimizing electronic interactions and active site density offers valuable strategies for the broader development of efficient and durable electrochemical systems.

In summary, the work of Professor Kangwoo Cho's team represents a significant advancement in electrochemical engineering, combining fundamental research with practical solutions. By addressing challenges in wastewater management and renewable energy production, their scalable NFI/TiO₂ anode design sets a benchmark for future developments. As global demand for sustainable water and energy technologies continues to grow, the methodologies and findings from this research are poised to drive further innovations in material science and environmental engineering.