Shape–Preserved CoFeNi–MOF/NF Exhibiting Superior Performance for Overall Water Splitting across Alkaline and Neutral Conditions

Abstract

This study reported a multi–functional Co0.45Fe0.45Ni0.9–MOF/NF catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting, which was synthesized via a novel shape–preserving two–step hydrothermal method. The resulting bowknot flake structure on NF enhanced the exposure of active sites, fostering a superior electrocatalytic surface, and the synergistic effect between Co, Fe, and Ni enhanced the catalytic activity of the active site. In an alkaline environment, the catalyst exhibited impressive overpotentials of 244 mV and 287 mV at current densities of 50 mA cm−2 and 100 mA cm−2, respectively. Transitioning to a neutral environment, an overpotential of 505 mV at a current density of 10 mA cm−2 was achieved with the same catalyst, showing a superior property compared to similar catalysts. Furthermore, it was demonstrated that Co0.45Fe0.45Ni0.9–MOF/NF shows versatility as a bifunctional catalyst, excelling in both OER and HER, as well as overall water splitting. The innovative shape–preserving synthesis method presented in this study offers a facile method to develop an efficient electrocatalyst for OER under both alkaline and neutral conditions, which makes it a promising catalyst for hydrogen production by water splitting.

Avoid Using Phosphate Buffered Saline (PBS) as an Electrolyte for Accurate OER Studies

“…The composition of “1×” PBS is shown in Table S2, with “saline” alluding to the major component, sodium chloride (NaCl). Recently, it has gained popularity as an electrolyte in assessing the performance of newly developed OER catalysts under neutral condition. − A standard 1× PBS solution has a reasonably good ionic strength of 0.156 M, providing adequate ionic conductivity for electrochemical reactions. The presence of phosphate buffer provides a fast reactant supply (OH – ) and reduces local pH shift during OER, better revealing the intrinsic catalytic properties.…”

“…The prevalent use of “0.1/1 M PBS” in the water electrolysis community often lacks composition details, − with “PBS” sometimes being used without specifying its full name. − This leads to misinformation within the water electrolysis community, as it could either denote pure phosphate buffer solution − or phosphate buffered saline, − which have different salt compositions, ionic strengths and ionic conductivities. Such lack of clarity poses complication and misinformation during cross-referencing among researchers. , Furthermore, denoting concentration using molarity is only correct for pure phosphate buffer solution, but not for phosphate buffered saline.…”