酸性溶液中Fe2+ /Fe3+相互转换对电极还原行为的影响

采用线性扫描伏安法和循环伏安法研究了含有Cl^-、SO₄^2-的酸性溶液中Fe²⁺/Fe³⁺相互转换对电极反应和Fe³⁺还原过程的影响. 结果表明: [Fe]_T=1 mol·L-1条件下，溶液中Fe³⁺/Fe²⁺的还原析出过程经过两个阶段：(1) E=0.35 V左右Fe³⁺还原成Fe²⁺过程; (2) E=-0.3 V之后H+的还原同时Fe²⁺离子与OH^-相结合生产Fe(OH)₂; Fe³⁺/Fe²⁺的相互转化主要影响Fe³⁺的第一还原阶段的还原峰电流和峰电位. |ipa/ipc|值随c(Fe³⁺ )/c(Fe²⁺ )增大而增大，且扫描速度慢时影响大，扫描速度快时影响小; 0.50 mol·L^-1 Fe²⁺+0.50 mol·L^-1 Fe³⁺时，随扫描速率的变化|ipa/ipc|值变化最小(|i_pa/i_pc|≈1.20). 同时，c(Fe³⁺ )/c(Fe²⁺ )也影响平衡电位，平衡电位随c(Fe³⁺ )/c(Fe²⁺ )增大而正移，电位从E₁=0.501 V升至E₅=0.565 V.

Effect ofFe2+/Fe3+Interconvertion on Reduction Behavior of Fe3+ in Acidic Electrolytes

The influences of ferrous/ferric (Fe²⁺/Fe³⁺) interconvertion on electrochemical reduction and electrode reaction ofFe³⁺ were investigated by using linear sweep voltammetry, potentiostatic method and cyclic voltammetry (CV) in acidic electrolytes containing chloride ion (Cl^- ) and sulfate ion (SO₄^2-). It was shown that the reduction process ofFe³⁺/Fe²⁺ would take place in two independent stages: (1) the reduction ofFe³⁺ toFe²⁺ at E=0.35V and (2) the co-precipitation ofFe²⁺ by forming Fe(OH)₂ (E≤-0.3 V) instead of Fe. The major effect ofFe²⁺/Fe³⁺ interconvertion on the reduction is the |ipa/ipc| of quasi-reversible and equilibrium potential in the first stage. Practically speaking, the |ipa/ipc| values increased with the increase ofc(Fe³⁺ )/c(Fe²⁺ ), and the values of |ipa/ipc| at fast sweep rates were less strongly affected than those at slow sweep rates. The least variation in |ipa/ipc| (|i_pa/i_pc|≈1.20) with sweep rate was observed in 0.50mol·L^-1Fe²⁺ and 0.50mol·L^-1Fe³⁺ solutions. Meanwhile, the equilibrium potential was also affected byc(Fe³⁺ )/c(Fe²⁺ ). The equilibrium potential shifted more positively from E₁=0.501 V in No. ① to E₅=0.565 V in No. ⑤ among the five samples studied in this work.