Citation: Taobo Huang, Haodong Ji, Xiuping Zhu. Understanding salinity gradient energy recovery with hexacyanoferrate electrodes based on first-principles[J]. Chinese Chemical Letters, ;2026, 37(11): 112579. doi: 10.1016/j.cclet.2026.112579 shu

Understanding salinity gradient energy recovery with hexacyanoferrate electrodes based on first-principles

Taobo Huang ^a ,
Haodong Ji ^b ,
Xiuping Zhu ^{a, c, *,}

a.
Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China
b.
School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China
c.
Institute of Eco-Chongming (IEC), Shanghai 202151, China

xpzhu@fudan.edu.cn

Received Date: 10 June 2025
Revised Date: 9 December 2025
Accepted Date: 3 March 2026
Available Online: 4 March 2026

Figures(5)

Transition metal hexacyanoferrates (MHCFs) have emerged as attractive materials for salinity gradient (SG) energy recovery. However, inconsistent evaluation methods have hindered systematic material selection. First–principles calculations were carried out to identify electronic structure determinants of voltage profiles and reaction stability in four MHCF variants (M = Mn, Ni, Cu, Zn), with emphasis on partial Na⁺ deintercalation under SG. It was found that d orbital interactions controlled redox performance: t_2g orbitals governed voltages in Mn, Ni, and Zn systems, whereas Cu exhibited coupled t_2g and e_g behavior. CuHCF and NiHCF were predicted to deliver voltages above 1.26 V due to combined Fe³⁺/Fe²⁺ and Mⁿ⁺/M^(n-1)+ redox processes. In contrast, MnHCF and ZnHCF were limited to voltages below 0.87 V owing to single–pair redox activity. Experimental validation using coprecipitation synthesized MHCFs confirmed these predictions; cyclic voltammetry measurements matched the theoretical redox assignments. A design principle was thus established: Participation of e_g orbitals in transition metal centers enhances theoretical voltage. This study bridges fundamental d orbital physics and practical electrode design for SG energy conversion.
- Salinity gradient energy,
- Hexacyanoferrate,
- First-principles calculation,
- 3d transition metals,
- Concentration flow cells
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