In-situ activation of three-dimensional porous NiFe alloy: Synergistic NiFe hydroxide/alloy as composite active sites for efficiently catalyzing alkaline water splitting

• Published in: Journal of alloys and compounds 2024-08, Vol.997, p.174942, Article 174942
• Main Authors: Tian, Xueqing, Wang, Yanhui, Sun, Fanjia, Zhu, Rui, Han, Mingyue, Zang, Jianbing
• Format: Article
• Language: English
• Subjects: Composite active sites; In-situ activation; Porous NiFe alloy; Water splitting
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2024.174942

The strategic engineering of bifunctional catalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media is critical for water-splitting technologies. This study presented a catalyst consisting of in situ grown nickel iron (NiFe) hydroxide/porous alloy composite catalytic sites on a nickel foam (NF) substrate. Initially, a porous NiFe alloy was electrodeposited onto NF, employing hydrogen (H2) bubbles as dynamic templates to induce a three-dimensional (3D) architecture. Subsequently, ultrathin layers of NiFe hydroxide nanosheets were synthesized in situ via electrochemical activation. The distinctive porous structure, coupled with the in-situ activated nanosheets, augmented the exposure of active sites, optimized electrolyte interaction, and expedited the expulsion of gaseous byproducts, collectively enhancing the kinetics of water electrolysis. The resultant a-Ni2Fe/NF demonstrated superior OER/HER activities, achieving overpotentials of merely 240 mV for OER and 183 mV for HER at a current density of 100 mA cm-2 in alkaline solution. Moreover, a voltage of just 1.53 V was requisite to attain a current density of 10 mA cm-2 for overall water splitting. Operando Raman spectroscopy revealed the formation of NiOOH and FeOOH active phases during HER, indicating the hydroxide’s role in adsorbing hydroxyl groups and shielding NiFe alloy’s H* adsorption sites from oxidation. The presence of the more reactive β-NiOOH phase was discerned during OER process, acting as an intermediate. This straightforward yet efficacious strategy heralded a new paradigm in the design of NiFe-based bifunctional catalysts, significantly bolstering the efficiency of water electrolysis catalysis. [Display omitted] •Preparation of porous NiFe alloy using dynamic hydrogen bubble template.•In-situ activation of alloy to obtain ultra-thin hydroxide.•The a-Ni2Fe/NF exhibits overpotentials of 240/183 mV at 100 mA/cm2 for OER/HER.•The composite HER active sites are used for H* and OHad adsorption respectively.