Insight into the amorphous nickel-iron (oxy)hydroxide catalyst for efficient oxygen evolution reaction.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Nickel-iron (oxy)hydroxides (NiFeO_x(OH)_y) are promising electrocatalysts for the oxygen evolution reaction (OER).
• The precise roles of nickel (Ni) and iron (Fe) in NiFeO_x(OH)_y during OER remain debated, particularly regarding the dominant active site.

Purpose of the Study:

• To investigate the atomic ratio of Ni and Fe in NiFeO_x(OH)_y catalysts to determine the dominant active site for OER.
• To elucidate the synergistic roles of Ni and Fe in enhancing OER performance.

Main Methods:

• Electrochemical characterization of NiFeO_x(OH)_y catalysts with varying Ni/Fe atomic ratios.
• Analysis of Tafel slopes to identify the active catalytic sites.
• Performance evaluation including overpotential, current density, and long-term stability.

Main Results:

• Catalysts containing Fe species exhibited significantly lower Tafel slopes (around 40 mV dec^-1) compared to those without Fe.
• The optimal Ni/Fe atomic ratio (1:1.18) demonstrated exceptional OER performance, requiring only 250 mV overpotential for 10 mA cm^-2 and a Tafel slope of 39 mV dec^-1.
• The optimized catalyst maintained stability for 50 hours at 50 mA cm^-2 with minimal potential decay.

Conclusions:

• Iron (Fe) sites are identified as the dominant active sites in NiFeO_x(OH)_y for the oxygen evolution reaction.
• Nickel (Ni) species play a crucial role in adsorbing hydroxide ions (OH^-), which benefits the Fe active sites and improves overall OER efficiency.
• The study provides critical insights into the functional roles of Ni and Fe in NiFeO_x(OH)_y, guiding the rational design of advanced OER electrocatalysts.