Periodic Reporting for period 1 - DIMCO (Development and Investigation of Manganese-doped NiFe nanosheet Catalyst for Oxygen Evolution Reaction)
Reporting period: 2019-04-01 to 2021-03-31
Fossil fuels (e.g. coal, gasoline and natural gas etc.) serve as the dominant energy source for electricity generation, heating, transportation and so on, as they are cheap and abundant, accounting for approximately 80% of the world energy supply. However, the use of this carbon source is finite and leads to emissions including a lot of toxic air pollutants and carbon dioxide (CO2) which has been established as one of the most critical driving forces of climate change. Negative impacts of the climate change have been already visible, including increase of sea level, ocean acidification as well as harm to human health. Until we get out of the fossil fuel dependence, such terrible consequences will be continued and grow as a significant threat to our future generations.
Hydrogen (H2) has been paid much attention as an alternative energy source to the fossil fuels. H2 is directly used as a fuel for Fuel Cell systems to generate electricity and moreover it is used as a precursor for making useful chemicals such as alcohols, ammonia and various organic compounds. Although currently steam methane reforming accounts for the majority of hydrogen production, generating inevitably CO2, H2 can be also produced from water (H2O), avoiding any harmful emissions, which is what’s called electrochemical water splitting. During the water electrolysis, hydrogen evolution reaction (HER) at cathode and oxygen evolution reaction (OER) at anode take place at the same time and the overall system efficiency is highly dependent of the capability of anode catalyst to promote OER due to its slow reaction rate compared with the HER. Precious noble-metal-based materials such as ruthenium oxide (RuO2) and iridium oxide (IrO2) have exhibited high catalytic activity and stability for the OER at a wide range of pHs. Nonetheless, they are fairly rare and costly for a large scale application and hence considerable efforts have been dedicated to developing cheap and active catalysts that are made of earth-abundant materials such as nickel (Ni), cobalt (Co) and iron (Fe). NiFe-based (oxy)hydroxide among their combinations is widely studied and well known as a benchmark catalyst. In order to further improve the performance and guide rational design of NiFe oxides catalysts, this project aims to study fundamental questions of which metal is more responsible for the OER activity between Ni and Fe by using diverse analysis techniques. As a result, it is proved that Ni and NiFe catalyze the OER in different ways and Fe-dependent structural change plays an important role in the OER activity. Moreover, a possible way of using FeOOH in the form of nanocluster on the surface of NiOOH is suggested to achieve improvement of the OER performance over the benchmark NiFe oxides.
Hydrogen (H2) has been paid much attention as an alternative energy source to the fossil fuels. H2 is directly used as a fuel for Fuel Cell systems to generate electricity and moreover it is used as a precursor for making useful chemicals such as alcohols, ammonia and various organic compounds. Although currently steam methane reforming accounts for the majority of hydrogen production, generating inevitably CO2, H2 can be also produced from water (H2O), avoiding any harmful emissions, which is what’s called electrochemical water splitting. During the water electrolysis, hydrogen evolution reaction (HER) at cathode and oxygen evolution reaction (OER) at anode take place at the same time and the overall system efficiency is highly dependent of the capability of anode catalyst to promote OER due to its slow reaction rate compared with the HER. Precious noble-metal-based materials such as ruthenium oxide (RuO2) and iridium oxide (IrO2) have exhibited high catalytic activity and stability for the OER at a wide range of pHs. Nonetheless, they are fairly rare and costly for a large scale application and hence considerable efforts have been dedicated to developing cheap and active catalysts that are made of earth-abundant materials such as nickel (Ni), cobalt (Co) and iron (Fe). NiFe-based (oxy)hydroxide among their combinations is widely studied and well known as a benchmark catalyst. In order to further improve the performance and guide rational design of NiFe oxides catalysts, this project aims to study fundamental questions of which metal is more responsible for the OER activity between Ni and Fe by using diverse analysis techniques. As a result, it is proved that Ni and NiFe catalyze the OER in different ways and Fe-dependent structural change plays an important role in the OER activity. Moreover, a possible way of using FeOOH in the form of nanocluster on the surface of NiOOH is suggested to achieve improvement of the OER performance over the benchmark NiFe oxides.
A custom-made electrochemical cell was developed for real-time in situ observation of chemical and structural changes in Ni and NiFe LDHs by using Raman spectroscopy, well known for its sensitivity to vibrations of metal oxygen bonds. First of all, we confirmed that lattice oxygens of Ni LDH participate in the oxygen evolution reaction process, while no participation of lattice oxygens was observed for NiFe LDH. Moreover, we found that the NiFe lattice gets more disordered as Fe is more added and consequently there is a relationship between the lattice disorder and OER activity. In other words, we proposed optimizing lattice order as a strategy to improve the OER performance of NiFe LDH catalyst. These results have been presented at an international conference and also published through a high impact peer-reviewed journal.
According to previous reports, it turned out that if Fe is too much added to Ni-based oxides, FeOOH begins to form in the bulk layer, resulting in decrease of the OER activity. However, we revealed that FeOOH nanoclusters are much more active for the OER than NiFe LDH, if the FeOOH is formed and distributed on the surface of NiOOH (oxidized form of Ni oxides) but not inside of the catalyst layer. By using Raman spectroscopy, the FeOOH-NiOOH catalyst was monitored in real time during the OER process and finally the relevant mechanism was experimentally proved for the first time. In this mechanism, Fe was thought of as an oxygen evolving site and helped to proceed by the neighboring Ni site. The result was published in a world-leading peer-reviewed journal.
In addition to such Fe-containing Ni based oxides, Co oxide, one of the most promising candidates for alkaline OER, was also studied during the project. By using operando surface enhanced Raman spectroscopy, we found for the first time that a superoxide intermediate exists in the catalytic cycle of OER on the Co oxide and it is likely originated from both hydroxide anions of electrolyte and lattice oxygens. Based on the experimental finding, we proposed a mechanism where lattice oxygens participate directly in the OER and the rate-determining step (RDS) is liberation of the oxygen molecule rather than O-O bond formation that has been generally known as RDS. This work was presented in an international conference and then published through a world-leading peer-reviewed journal.
High entropy fluoride, a new class of materials recently developed, was studied in terms of synthetic method and its application. A simple mechanochemical way of synthesizing high entropy fluorides containing possibly 4 to 7 transition metals (Co, Cu, Mg, Ni, Zn, Mn, and Fe) in equiatomic ratios was successfully developed and the newly synthesized samples were used to see a potential application to oxygen evolution reaction. The OER performance was more active over a state of the art noble metal catalyst, IrO2. The result suggests the mechanochemical synthesis of high entropy fluorides would be promising for electrocatalyst development. The result was published through a high impact peer-reviewed journal as open access article.
According to previous reports, it turned out that if Fe is too much added to Ni-based oxides, FeOOH begins to form in the bulk layer, resulting in decrease of the OER activity. However, we revealed that FeOOH nanoclusters are much more active for the OER than NiFe LDH, if the FeOOH is formed and distributed on the surface of NiOOH (oxidized form of Ni oxides) but not inside of the catalyst layer. By using Raman spectroscopy, the FeOOH-NiOOH catalyst was monitored in real time during the OER process and finally the relevant mechanism was experimentally proved for the first time. In this mechanism, Fe was thought of as an oxygen evolving site and helped to proceed by the neighboring Ni site. The result was published in a world-leading peer-reviewed journal.
In addition to such Fe-containing Ni based oxides, Co oxide, one of the most promising candidates for alkaline OER, was also studied during the project. By using operando surface enhanced Raman spectroscopy, we found for the first time that a superoxide intermediate exists in the catalytic cycle of OER on the Co oxide and it is likely originated from both hydroxide anions of electrolyte and lattice oxygens. Based on the experimental finding, we proposed a mechanism where lattice oxygens participate directly in the OER and the rate-determining step (RDS) is liberation of the oxygen molecule rather than O-O bond formation that has been generally known as RDS. This work was presented in an international conference and then published through a world-leading peer-reviewed journal.
High entropy fluoride, a new class of materials recently developed, was studied in terms of synthetic method and its application. A simple mechanochemical way of synthesizing high entropy fluorides containing possibly 4 to 7 transition metals (Co, Cu, Mg, Ni, Zn, Mn, and Fe) in equiatomic ratios was successfully developed and the newly synthesized samples were used to see a potential application to oxygen evolution reaction. The OER performance was more active over a state of the art noble metal catalyst, IrO2. The result suggests the mechanochemical synthesis of high entropy fluorides would be promising for electrocatalyst development. The result was published through a high impact peer-reviewed journal as open access article.
Water electrolysis only accounts for less than 5% of global industrial production of hydrogen due to the fact that still it is not cost-effective. Moreover, the alkaline water electrolysis using a commercial Ni electrode exhibits lower current efficiency than acidic water electrolysis using precious noble metal electrodes as the state of the art. Although our group had recently reported an unconventional OER catalyst consisting of FeOOH nanoclusters on NiOOH support, the relevant mechanism and detailed composition remained unclear. Now that we reveal the underlying features, the FeOOH-NiOOH catalyst is expected to gain much more attention due to the simple and facile preparation method as well as high performance. In that sense, the results of this project may encourage utilization and further development of the FeOOH-NiOOH catalyst that has high potential to displace the current commercial Ni electrode. Now we are in the first phase (2020-2024) of a large portfolio for the European Green Deal aiming to be climate neutral by 2050. Obviously, a renewable and sustainable production of hydrogen is at the heart of this long-term strategy. Hopefully our research achievements would contribute to industry as well as academia and lead to an important milestone in the hydrogen strategy for pursuing decarbonization.