Unveiling the role of Fe doping and Mo leaching in Fe-MoNi4@NiMoOx bifunctional catalysts for water splitting

Fe doping reduces the Volmer barrier of MoNi 4 to enhance HER activity. • Mo leaching induces reconstruction into active NiMoFeOOH@MoO 4 2- for OER. • The AEMWE using this catalyst as dual electrodes reaches low voltages at 500 and 1000 mA cm -2 . • The electrolyzer operates stably for over 200 h, revealing great application potential in water electrolysis. The hydrogen evolution reaction (HER) is fundamentally limited by the sluggish water dissociation step, while the oxygen evolution reaction (OER) is constrained by the reconstruction behavior of the catalyst under operating conditions. Herein, we report a Fe-doped NiMoO x nanoflower decorated with Fe-doped MoNi 4 nanoparticles (Fe-MoNi 4 @NiMoO x ). Density functional theory (DFT) calculations reveal that the incorporation of Fe lowers the Volmer step energy barrier for MoNi 4 , thereby boosting its HER performance. For the OER, Mo leaching drives the reconstruction of MoNi 4 into catalytically active NiMoFeOOH@MoO 4 2− . Furthermore, theoretical calculations confirm that Fe/Mo doping and adsorbed MoO 4 2− facilitate rapid electron transfer within NiMoFeOOH and reduce the energy barrier of the rate-determining step for the OER. As a result, the Fe-MoNi 4 @NiMoO x catalyst delivers exceptional HER and OER activities, with overpotentials as low as 102 and 212 mV for HER, and 278 and 343 mV for OER at current densities of 100 and 500 mA cm −2 , respectively, alongside excellent stability exceeding 100 h at 500 mA cm −2 . When employed as both the cathode and anode in an anion exchange membrane water electrolyzer (AEMWE), this catalyst achieves current densities of 500 and 1000 mA cm −2 at low cell voltages of 2.22 and 2.56 V, respectively, while maintaining stable operation for over 200 h at 500 mA cm −2 . Fe-MoNi 4 @NiMoO x nanoflower electrode was developed for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For HER, Fe incorporation lowers the Volmer step energy barrier of MoNi 4 , thereby boosting its HER performance. For OER, Mo leaching induces reconstruction into NiMoFeOOH@MoO 4 2− , where Fe/Mo doping and MoO 4 2− adsorption synergistically enhance electron transfer and reduce the rate-determining step barrier. Download: Download high-res image (241KB) Download: Download full-size image