Theoretical Investigation of the Catalytic Activity of Goethite (α-FeOOH) for the Electrochemical Water Oxidation

Recently, to replace the expansive noble metals in electrocatalyst, transition metals with low cost and comparable performances are chosen as substitutes. Among transition metals, iron, which is one of the most abundant metal in the earth crust, is relatively out of the attention as an electrocatalyst. Due to its earth abundance and well-organized production system, iron has the one-tenth price of nickel, and even one-fiftieth price for cobalt. Considering that the ultimate goal of the water electrocatalysis system is an integrated system with a photovoltaic cell which demands the scale-up processing, the cost competitiveness can be maximized for the commercialization. To enjoy the strong cost competitiveness of the iron, the poor catalytic property of the iron based electrocatalysts, particularly its low current density should be enhanced. According to several studies, it is known that certain phase, iron oxyhydroxide, can have much higher current density than existing iron-based electrocatalysts. Especially, iron oxihydroxide (FeOOH) belongs to thermodynamically stable form among iron oxides and presented to have enhanced catalytic property by experiments. Though, there are not enough theoretical investigations on its catalytic activity. Herein, we investigate the water oxidation mechanism on the Iron oxyhydroxide(FeOOH) electrocatalysts using first-principles calculations based on Density Functional Theory. With calculations of relative surface stabilities and adsorbate coverages, the most stable low-index surfaces of FeOOH will be determined. Next, with the determined FeOOH surfaces, we will compare the theoretical overpotentials achieved by calculating each oxygen evolution reaction steps. For each step, the magnetic state will be checked for the explanation of oxygen evolution reaction process. Furthermore, impacts of the various dopants such as Mn, Ni, Co will be also investigated. With the calculation using hybrid functional, the electronic structure of the iron oxyhydroxide, with and without dopants, will be obtained and it will give the explanation of different OER catalytic activity shown by iron oxyhydroxide with different dopants. For the strict verification of the calculation data, experiment results of the bare and doped FeOOH will be also presented. All the alpha FeOOH samples are synthesized with electrodeposition method and their electrocatalytic properties will be evaluated. With the comparison of calculation and experiment data, it is expected to figure out how the dopants affect bulk properties, reaction at the surface of the FeOOH and eventually influence the electrocatalytic properties.