FeOOH Surface Research Articles

The surface electron transfer strategy promotes the hole of PDI release and enhances emerging organic pollutant degradation

In semiconductor photocatalysts, the easy recombination of photogenerated carriers seriously affects the application of photocatalytic materials in water treatment. To solve the serious problem of electron−hole pair recombination in perylene diimide (PDI) organic semiconductors, we loaded ferric hydroxyl oxide (FeOOH) on PDI materials, successfully prepared novel FeOOH@PDI photocatalytic materials, and constructed a photo-Fenton system. The system was able to achieve highly efficient degradation of BPA under visible light, with a degradation rate of 0.112 min−1 that was 20 times higher than the PDI system, and it also showed universal degradation performances for a variety of emerging organic pollutants and anti-interference ability. The mechanism research revealed that the FeOOH has the electron trapping property, which can capture the photogenerated electrons on the surface of PDI, effectively reducing the compounding rate of photogenerated carriers of PDI and accelerating the iron cycling and H2O2 activation on the surface of FeOOH at the same time. This work provides new insights and methods for solving the problem of easy recombination of carriers in semiconductor photocatalysts and degrading emerging organic pollutants.

Dense heterogeneous interfaces boost the electrocatalytic oxygen evolution reaction

Efficient and cost-effective catalysts are essential to drive the oxygen evolution reaction (OER) in sustainable hydrogen production through water splitting. In this study, we introduce an innovative strategy aimed at constructing heterogeneous structure that form abundant Fe2O3/NiSe2 interfaces on the FeOOH surface. The resulting catalyst exhibits extraordinary performance with an excellently low overpotential of 169 mV at 10 mA cm−2. Notably, this catalyst also demonstrates impressive long-term stability in alkaline seawater. Compared to traditional heterogeneous catalysts with core-shell structures, Fe2O3/NiSe2 possesses a closely heterogeneous interface, which plays a role in modulating the interface electron. Supported by complementary spectroscopy and theoretical calculations, it has been further demonstrated that the distinctive Fe-O-Ni-Se structure can effectively modulate the electronic state of Ni, thereby enhancing the adsorption of oxygen-containing intermediates and facilitating oxygen desorption. Overall, this research presents a promising avenue for enhancing the electrocatalytic performance by amplifying active sites at interfaces.

Electrosorption of uranium (VI) by sulfonic acid‑decorated FeOOH nanorods

The capacitive deionization (CDI) technology for the removal of U(VI) has been the focus of attention because of its superiorities in operation cost, energy consumption, and environmental friendliness. In this report, electrode materials based on sulfonic acid‑decorated FeOOH were applied to CDI and flow electrode capacitive deionization (FCDI) for the first time. The sulfonic acid‑decorated FeOOH nanorods presented a high electrosorption capability of U(VI) in the CDI system (709.4 mg g−1 at 1.2 V and pH = 4.0, based on Langmuir model), which may result from the coordinative surfaces as well as the mesoporous structures of FeOOH. The thermodynamic and kinetic behaviors of the electrosorption process can be well-fitted using the Freundlich and pseudo-second-order model. The effective electrosorption in the presence of Na+ competitive ions and recycling of adsorbents in the CDI system further demonstrated the potential application of sulfonic acid‑decorated FeOOH nanorods for the electrosorptive removal of U(VI) from radioactive wastewater. The electrosorption mechanism was determined to be a combined process that is composed of diffusion of the uranyl ions into the EDL and adsorption onto the surface of FeOOH via the coordination interaction from Fe-OH and sulfonic acid groups (-SO3H). Further, continuous FCDI batch experiments in low concentration of feed water (60 mg L− 1 U) show that removal efficiency of U remained over 99% in 10 times continuous cycles, endowing it more possibilities for capacitive deionization from research to practical application.

(Invited) P-Doped Hematite for Efficient Photoelectrochemical Water Splitting

In this talk, I would like to discuss about how a simple in-situ phosphorus (P) doping strategy improves the overall PEC performance of hematite. By introducing enriched FePO4 regions on the Ti-doped FeOOH surface and subsequent high-temperature annealing, P,Ti co-doped Fe2O3 (P,Ti-Fe2O3) nanorods were fabricated. P,Ti-Fe2O3 not only increased the conductivity by creating oxygen vacancies but also generated a porous structure inside the hematite. Benefiting from the efficient P doping effects, the resulting P,Ti-Fe2O3 photoanode exhibited 94% improved photocurrent density compared to that of Ti-Fe2O3 (@ 1.23 VRHE) under 1 sun illumination. After applying the co-catalyst, NiFeOx/P,Ti-Fe2O3showed significantly enhanced photocurrent density (3.54 mA cm-2 at 1.23 VRHE) with a 108 mV cathodic shift. Our study suggests a new approach for achieving porous hematite and a highly efficient PEC system by a simple and cost-effective nonmetal P-doping method.

Investigation of hybrid plasma-catalytic degradation of toluene over FeOOH/γ-Al2O3 catalysts

In the present study, FeOOH/γ-Al2O3 catalyst was first introduced into dielectric barrier discharge (DBD) plasma-catalysis system for toluene degradation, and its catalytic performance and mechanism were studied. It was found that the toluene degradation efficiency, energy yield (EY), and COx selectivity were significantly improved in the plasma-FeOOH/γ-Al2O3 system by comparison to the plasma-only process. The ozone concentration detected in this study decreased significantly in plasma-FeOOH/γ-Al2O3 system, which could be concluded that the ozone catalytic process played an important role in the plasma-FeOOH/γ-Al2O3 system for toluene degradation. The toluene and intermediates adsorbed on the surface FeOOH catalysts could react with O* from O3 decomposition and Oads derived from oxygen vacancies, which was conducive to an improved degradation and mineralization performance. Besides, the transformation of O3 to·OH on FeOOH surface was considered as one of the main mechanisms for enhancing toluene degradation when the relative humidity of the background gas was increased from 30% to 50%. The key process parameters, including specific energy input (SEI), catalyst loading, and oxygen content of the background gas, were optimized by response surface methodology (RSM) integrated Box-Behnken design (BBD). The results showed that oxygen content of the background gas was the most significant factor affecting the degradation efficiency of toluene, while energy yield was mainly determined by SEI. The possible toluene degradation pathways in plasma-FeOOH/γ-Al2O3 system were proposed according to the identification of intermediates using GC-MS.

Activation of Dolomite Flotation by Ferrous Hydroxide and Carbonate

The major problem with Carlin-type gold deposit flotation is that the high dolomite content in the concentrate decreases the quality of gold. Further, the activation mechanisms involved in dolomite flotation are still not fully understood. Herein, the correlation of Fe2+ conversion with xanthate adsorption and dolomite flotation was investigated to reveal the effect of dolomite embedded with pyrite. Flotation tests suggested that Fe2+ rather than Fe3+ improved the floatability of dolomite from 20% to 45%. Contact angles and thermodynamic tests indicated that the hydrophobicity of Fe2+-modified dolomite corresponds to the adsorption of xanthate. Importantly, time-of-flight secondary ion mass spectroscopy (Tof-SIMS) and x-ray photoelectron spectroscopy (XPS) attributed the activation of dolomite flotation to the formation of Fe(OH)2 and FeCO3. The coordination model of flotation successfully elucidated the selective adsorption of xanthate between Fe(OH)2, FeCO3 and FeOOH surfaces. The density function theory (DFT) simulation calculation was performed to identify the reaction rate at the atomic level, and the density of states (DOS) was also conducted to verify the conclusions at the electronic level. This study presents important surface chemistry evidence for understanding and regulating the poor selectivity in the flotation of Carlin-type gold deposits.

Enhanced removal of aqueous Cr(VI) by the in situ iron loaded activated carbon through a facile impregnation with Fe(II) and Fe(VI) two step method: Mechanism study.

In this study, a novel in situ iron-loaded activated carbon (AFPAC) was prepared by a FeSO4/K2FeO4 impregnation and oxidation combination two-step supported on activated carbon for enhanced removal of Cr(VI) from aqueous solutions. Cr(VI) removal efficiency greatly increased by AFPAC more than 70% than that of fresh activated carbon (AC), which is due to rich iron oxides formed in situ and the synergistic effect between iron oxides and activated carbon. Cr(VI) adsorption behaviors on AFPAC under different water quality parameters were investigated. The maximum monolayer adsorption capacities for Cr(VI) by AFPAC are as high as 26.24mg/g, 28.65mg/g, and 32.05mg/g at 25°C, 35°C and 45°C at pH 4, respectively. Density functional theory (DFT) results showed that the adsorption energy of K2Cr2O7 on the surface of FeOOH was - 2.52eV, which was greater than that on the surface of bare AC, and more charge transfer occurred during the adsorption of K2Cr2O7 on the surface of FeOOH, greatly promoting the formation of Cr = O-Fe. Cr(VI) removal by AFPAC included electrostatic attraction, redox reaction, coordinate complexation, and co-precipitation. Cr(VI) adsorption process on AFPAC consisted of the three reaction steps: (1) AFPAC was fast protonation and Cr2O72- would electrostatically attract to the positively charged AFPAC surface. (2) Cr2O72- was reduced into Cr2O3 by the carbons bond to the oxygen functionalities on activated carbon and the redox reaction process of FeSO4 and K2FeO4. (3) The inner-sphere complexes were formed, and adsorbed on AFPAC by iron oxides and then co-precipitation.

Meso-pore generating P doping for efficient photoelectrochemical water splitting

Hematite (Fe2O3) has been widely used as a photoanode in photoelectrochemical water splitting (PEC) for green hydrogen production. Here, for the first time, we investigate how a simple in-situ phosphorus (P) doping strategy improves the overall PEC performance of hematite with a systematic analysis of the various effects on the PEC performance. By introducing enriched FePO4 regions on the Ti-doped FeOOH surface and subsequent high-temperature annealing via P-doping, meso-porous P,Ti co-doped Fe2O3 (P,Ti-Fe2O3) nanorods were fabricated. P,Ti-Fe2O3 exhibited four-fold and two-fold increased BET surface area and electrical active area, respectively, compared to that of Ti-Fe2O3. Benefiting from the nano-structuring and efficient P doping effects [e.g., increased carrier density (Nd=3.48168 ×1020 cm−3), enhanced charge separation (ηbulk= 38.7% and ηsurface= 79.1%), and steeper band bending (Wd=3.910 nm)], the resulting P,Ti-Fe2O3 photoanode exhibited 94% improved photocurrent density of 2.50 mA cm−2 compared to that of Ti-Fe2O3 (@ 1.23 VRHE) under 1 sun illumination. With the deposition of the NiFeOx cocatalyst, the NiFeOx/P,Ti-Fe2O3 photoanode exhibited excellent photocurrent density of 3.54 mA cm−2 (@ 1.23 VRHE) with a remarkable cathodic shift (180 mV) of the onset potential, marking the highest value among P doped hematite studies. This study suggests a new paradigm of P doped hematite with mesopores and gradient doping properties affordable in a cost-efficient way, achieving an excellent PEC water splitting performance.

(Invited) Non-Metal P Doping for Efficient Water Splitting

Here, we investigate how a simple in-situ phosphorus (P) doping strategy improves the overall PEC performance of hematite. By introducing enriched FePO4 regions on the Ti-doped FeOOH surface and subsequent high-temperature annealing, P,Ti co-doped Fe2O3 (P,Ti-Fe2O3) nanorods were fabricated. P,Ti-Fe2O3 not only increased the conductivity by creating oxygen vacancies but also generated a porous structure inside the hematite. Benefiting from the efficient P doping effects, the resulting P,Ti-Fe2O3 photoanode exhibited 94% improved photocurrent density compared to that of Ti-Fe2O3 (@ 1.23 VRHE) under 1 sun illumination. After applying the co-catalyst, NiFeOx/P,Ti-Fe2O3 showed significantly enhanced photocurrent density (3.54 mA cm-2 at 1.23 VRHE) with a 108 mV cathodic shift. Our study suggests a new approach for achieving porous hematite and a highly efficient PEC system by a simple and cost-effective nonmetal P-doping method.

Surface modification and structure analysis of coated iron oxide yellow pigments to improve dispersion in organic solvents

For improving the dispersion of iron oxide yellow pigments (FeOOH) in organic solvents, a layer of silica was coated on the surface of FeOOH, and then further modified by silane coupling agent, as a heterogeneous coating was formed on the surface of FeOOH. The modified FeOOH was characterized by TEM, XRD, IR, XPS, TG‐DTA, and zeta potential. The dispersibility of modified FeOOH under different conditions was also studied. After coating and modification, a coating layer about 5 nm was formed on the surface of FeOOH. XRD results showed that sodium silicate and KH560 modified did not change crystal structure of FeOOH, even the SiO2 coating layer existed in amorphous form. The FeOOH was bound with SiO2 and silane coupling agent by chemical bond, based on the IR and XPS analysis. The heat resistance of FeOOH was slightly improved after coating. When the amount of SiO2 modified in surface coating was 8% of the mass of FeOOH, the modification time range from 1 to 1.5 h, temperature was between 60°C and 80°C, the pH value was 7–8, and the dispersibility of FeOOH in water was significantly improved. The zeta potential test showed that the surface of FeOOH/SiO2 was negative, and its dispersibility in water was improved because the absolute value of zeta potential increased. The dispersibility of FeOOH/SiO2 was related to the structure of coupling agent. After modification with KH560, the dispersion rate increased from 14.49% to 88.0%, which improved the dispersibility in organic solvents.

Fe(Co)OOH Dynamically Stable Interface Based on Self-Sacrificial Reconstruction for Long-Term Electrochemical Water Oxidation.

FeOOH on the real catalytic interface for the oxygen evolution reaction (OER) is chemically unstable to dissolve in alkaline media. Herein, based on the perspective of the dynamically stable interface, we purposely design the well-dispersed nanorod arrays of CoMoO4 as a host on activated iron foam (IF) to realize the optimal redeposition of FeOOH, constructing a self-sacrificial template rich in the FeOOH surface. Notably, at long-time oxidation potential, the precatalyst FeOOH-CoMoO4 can realize MoO42- dissolution and redeposition of Co oxyhydroxides on FeOOH host simultaneously, constructing a dynamically stable Fe(Co)OOH interface. The introduction of CoOOH improves conductivity and provides synergistic effect with FeOOH to lower the energy barrier for OER and maintain long-time stability, eventually exhibiting a low overpotential of 298 mV to reach the current density of 100 mA cm-2 and high stability over 60 h. This work demonstrates the feasibility of manipulating metal dissolution-redeposition process for a dynamically stable interface.

Mesoporous goethite for rapid and high-capacity fluoride removal from drinking water

Fluoride (F) contamination is widely distributed due to natural or anthropogenic causes. A series of mesoporous goethite (α-FeOOH) were synthesized by hydrothermal treatment for rapid F removal from water. The morphology of adsorbents was found to be controlled by varying the hydrothermal and calcination conditions. A highly crystallized FeOOH can be prepared at hydrothermal temperature of 80 °C without further calcination. The sorption isotherm data could be adequately described by Freundlich model and kinetic data followed pseudo-second-order kinetic model. The highest adsorption capacity is as high as 80.1 mg/g. Mesoporous FeOOH exhibited high adsorption capacity in a wide pH range of 3–10 with final pH falling into a stable range (pH 5–6). The presence of Cl- and NO3- seldom impacted the adsorption performance, while addition of high concentrations of CO32- and PO43- (30 mg/L) weakened the adsorption capacity up to 18.2%. For the recycle tests with real F-contaminated groundwater, the removal efficiency dropped slightly from 93.1% (at cycle 1) to 91.8% (at cycle 5), suggesting the adsorbents is powerful for practical use. The FTIR, SEM, and XPS characterization results all confirmed the adsorption of F and revealed that the major adsorption mechanism is the ion-exchange between F ions and hydroxyl groups on the surface of FeOOH.

FeOOH/Ni heterojunction nanoarrays on carbon cloth as a robust catalyst for efficient oxygen evolution reaction

Developing catalysts based on transition metal-based materials for oxygen evolution reaction (OER), which are cheap and efficient, is one of the keys to increase the rate of electrolysis of water to produce hydrogen. Herein, we successfully synthesize iron hydr(oxy)oxide nano-arrays on carbon cloth (FeOOH@CC), and then metallic nickel is electrodeposited on its surface to fabricate FeOOH/Ni heterojunction nanoarrays. Notably, the optimal FeOOH/Ni heterojunction nanoarrays catalyst shows high electrocatalytic performance toward OER with a small overpotential of 257.8 mV at 50 mA cm−2, a Tafel slope of 30.8 mV dec−1 and outstanding long-term stability in alkaline media. The superior OER performance could be ascribed to the introducing of metallic nickel. The nickel in-situ grows on the surface of FeOOH, which not only can improve the conductivity of FeOOH, but also cooperate with FeOOH to form the FeOOH/Ni heterogeneous interfaces for further enhancing OER electrocatalytic activities. This work provides a simple and efficient strategy of interface engineering to fabricate oxyhydroxide/metal heterojunction nanoarrays as high-efficiency OER catalysts.

Adsorption of Organic Acids and Phosphate to an Iron (Oxyhydr)oxide Mineral: A Combined Experimental and Density Functional Theory Study.

The interaction of soil organic matter with mineral surfaces is a critical reaction involved in many ecosystem services, including stabilization of organic matter in the terrestrial carbon pool and bioavailability of plant nutrients. Using model organic acids typically present in soil solutions, this study couples laboratory adsorption studies with density functional theory (DFT) to provide physical insights into the nature of the chemical bonding between carboxylate functional groups and a model FeOOH cluster. Topological determination of electron density at bond critical points using quantum theory of atoms in molecules (QTAIM) analysis revealed that the presence of multiple bonding paths between the organic acid and the FeOOH cluster is essential in determining the competitive adsorption of organic acids and phosphate for FeOOH surface adsorption sites. The electron density and Laplacian parameter values from QTAIM indicated that the primary carboxylate-FeOOH bond was more ionic than covalent in nature. The experimental and computational results provide molecular-level evidence of the important role of electrostatic forces in the bonding between carboxylic acids and Fe-hydroxides. This knowledge may assist in the formulation of management studies to meet the challenges of maintaining ecosystems services in the face of a changing climate.

β-FeOOH catalyzed peroxymonosulfate for organic pollutant degradation in water: radical and non-radical mechanism

Iron-based catalysts as peroxymonosulfate (PMS) activator are commonly used to oxidize and degrade azo dye. However, there are still some issues such as low catalytic performance, relatively less reactive oxygen species and high metal iron dissolution. As such, a novel iron oxyhydroxide (FeOOHs) with four crystal form was synthesized and employed as efficient PMS activator for AO7 degradation in this study. It was found that the crystal form of catalyst had significant influence on its catalytic performance. β-FeOOH exhibited the best catalytic performance, owing to its smallest lattice size, maximum specific surface area and highest surface hydroxyl density. β-FeOOH/PMS system possessed a great high apparent reaction rate constant (1.3919 h−1), which was about 17, 3, 31, 20, 14, 49 and 23 times higher than that in β-FeOOH/persulfate(PS), Fe0/PMS, Fe0/PS, Fe2O3/PMS, Fe2O3/PS, Fe3O4/PMS and Fe3O4/PS system, respectively. More importantly, radical quenching tests and Electron spin resonance (ESR) analysis revealed that OH., SO4.−, O2.− and 1O2 were involved in the reaction process. The catalytic mechanism proposed that β-FeOOH had the effective electron transfer rate performance, and Fe3+ underwent a reduction to Fe2+ during the β-FeOOH/PMS catalytic oxidation process. Then, the regeneration of Fe2+ on the hydroxylated surface of FeOOH promoted the formation of FeOH+, which was crucial for PMS activation and reactive oxygen species (ROS) generation. The recyclability tests proved good stability and reusability of β-FeOOH. This study provides a kind of new understanding of peroxymonosulfate activation for environmental remediation and advances the study of iron-based oxyhydroxide in heterogeneous catalysis.

Visible-light-driven selective oxidation of methane to methanol on amorphous FeOOH coupled m-WO3

Direct conversion of methane into value-added fuels or chemicals under ambient conditions remains a great challenge. Constructing solar-energy-driven catalytic systems is considered as a promising strategy, but the conversion efficiency and products selectivity are still low, especially for producing alcohol derivatives. Herein, to promote the photocatalytic activity of methane partial oxidation to methanol, a series of FeOOH/m-WO3 consisting of ordered mesoporous WO3 (m-WO3) and highly dispersed amorphous FeOOH were synthesized by using KIT-6 silica as hard template. The prepared FeOOH/m-WO3 catalysts exhibit dramatically improved visible-light catalytic activities toward selective oxidation methane into methanol in the presence of H2O2. A methane conversion rate of 238.6 μmol·g−1·h−1 is achieved over the optimal 1.98% FeOOH/m-WO3, which is 3 times higher than that of pristine m-WO3 (79.2 μmol·g−1·h−1). Moreover, a methanol production rate of 211.2 μmol·g−1·h−1 with a selectivity of 91.0% is obtained on the optimum catalyst under 4 h visible-light irradiation. Significantly, the greatly improved methane conversion and methanol production can be attributed to efficient electron migration from the conduction band of m-WO3 to highly dispersed FeOOH, evidenced by in-situ XPS analysis, transient photocurrent response and photoluminescence spectra. Furthermore, based on radicals trapping experiments and electron spin resonance (ESR) results, methane is primarily activated by photoholes accumulated on the valence band of m-WO3 to generate methyl radicals (·CH3) and the produced hydroxyl radicals (·OH) via decomposing H2O2 by photoelectrons on FeOOH surface are predominant oxidant for methanol generation. Desired methanol is selectively produced via radicals reaction between ·CH3 and ·OH.

Correlation of surface oxidation with xanthate adsorption and pyrite flotation

Various studies have emphasized the importance of surface oxidation of sulfide minerals with regard to xanthate adsorption and their flotation response. However, the correlation between pyrite surface oxidation, xanthate adsorption and its flotation response has not been clearly established. The complexity lies in various intermediate sulfur oxidation products in different solution conditions. Thus, investigation of sulfur oxidation behavior is the key to understand pyrite oxidation. Ion chromatography (IC) and high performance liquid chromatography (HPLC) results showed an increase in the total amounts of occurring sulfur species with increasing slurry pH. Meanwhile, the ratio of S0/sulfur oxyanions was to become lower; X-ray Photoelectron Spectroscopy (XPS) identified the oxidized pyrite surface was rich in SO42− and FeOOH. Both the contact angle results and single mineral flotation data indicated that the more pyrite surface oxidized, the lower hydrophobicity and floatability were. Time-of-flight secondary ion mass spectroscopy (Tof-SIMS) was adopted to analyse xanthate adsorption on the surface of pyrite under conditions of either sufficient oxidation or on freshly polished surface which is assumed little oxidation. A significantly lower intensities of C4H9O and C4H9OCSS was found on the intensely oxidized pyrite surface, indicating xanthate adsorption had strong selectivity on FeS2 rather than FeOOH. The experimental results were further confirmed by theoretical calculation. The self-consistent charge density functional tight binding (SCC-DFTB) calculations indicated that the distances between the xanthate S atoms and surface Fe atoms of FeOOH were larger than the atomic radius of SFe. Essentially, the different electron configurations of their Fe atoms led to the selective adsorption of xanthate on FeOOH and FeS2 surfaces in terms of the coordination chemistry theory. This work provides valuable implications for understanding the correlation of surface oxidation, xanthate adsorption and its floatation behavior to mediate pyrite flotation.

Developing superior catalysts engineered by multichannel healing strategy for advanced oxidation

Catalyst deactivation derived from slow conversion of Fe(III)/Fe(II) is the critical problem restricting catalytic efficiency of advanced oxidation. Herein, a novel multichannel healing strategy is proposed for fast healing structural damage by designing rationally smart platform (TiO2-CDs-FeOOH hollow sandwich hybrid). This ingenious system shows remarkable catalytic activity (0.77 min−1) and stability towards the removal of organic contaminants. Systematic studies confirm that the excellent catalytic activity is attributed to multiple electron transfer (MET) behavior at interface between photocatalytic substrate and FeOOH, leading to highly efficient interfacial charge separation and then fast recovery of Fe(II) on FeOOH surface during H2O2 activation process. Notably, multichannel healing procedure and MET kinetic information are unveiled by UV–vis/scanning electrochemical microscopy (SECM) through an in situ probe scanning technique. A higher ET rate constant keff (0.92 × 10-2 cm s-1) was revealed over TiO2-CDs-FeOOH, two times that of TiO2-FeOOH, further confirming that multi-channel electron transfer could achieve fast Fe(III)/Fe(II) conversion. This work offers a new insight to design highly efficient catalysts for the practical applications of sustainable environmental remediation and energy conversion.

First principles calculations of surface dependent electronic structures: a study on β-FeOOH and γ-FeOOH.

We report a theoretical study on iron oxyhydroxide (FeOOH). The FeOOH surface is expected to act as an efficient electrochemical catalyst for the oxygen evolution reaction (OER), because it is based on iron, an element of the fourth highest Clarke number. Experimentally, the OER activity of β-FeOOH is known to be higher than that of γ-FeOOH. However, the details of the OER mechanism and the surface reactivities of the FeOOH polymorphs have not yet been fully understood. We performed first-principles calculations of bulk and surfaces of β-FeOOH and γ-FeOOH using density functional theory, to investigate their electronic structures and catalytic activities. The calculations suggest that depending on the surface indices, several surfaces may be favored for catalytic activities.

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.