Tag Archives: Electrochemical Synthesis

Shreya Mukherjee*, Gang Wu, University at Buffalo – SUNY, USA

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Sustainable synthesis of Ammonia (NH3) is gaining great attention not only for its use as an alternative renewable energy fuel but also to substitute production of distributed fertilizers through the conventional Haber Bosch process. The conventional Haber-Bosch process to produce NH3 uses fossil fuels in deriving hydrogen from steam reforming of natural gas, is energy intensive and also leads to significant CO2 emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) in alkaline medium saves the use of hydrogen as a reactant as the aqueous electrolyte forms the source of proton. However, the standard reduction potential of nitrogen and hydrogen fall in the same domain. Thus, hydrogen evolution reaction is so dominant at the applied potential that selectivity of nitrogen reduction is a major challenge in the budding field. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of the N2 molecule.

Herein, we report a comparative study of nitrogen adsorption on basic sites of different metal-organic framework. For certain MOFs, the central metal can be a basic site and for some others, the interplay between the organic ligand and the metal center can create basic sites. Despite the basic sites, it might not be easy to selectively reduce nitrogen in presence of protons in the electrolyte at the metal centers. We observed that MOF derived nitrogen-doped metal free nanoporous carbon electrocatalyst has a Faradaic efficiency (FE) greater than 10 % at -0.3 V vs RHE under ambient conditions for the NRR. ZIF8 derived nanoporous carbon exhibits a remarkable production rate of NH3 up to 3.4×10^-6 mol cm^-2 h^-1 using aqueous 0.1 M KOH electrolyte. Continue reading →

Helga Dogg Flosadottir, Arnar Sveinbjörnsson*, Atmonia, Iceland; Egill Skúlason, Fatemeh Hanifpour, Friðrik Magnus, Younes Abghoui, Jian Yang, University of Iceland, Iceland

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Density functional theory simulations have shed light on reaction mechanisms, rate limiting steps and minimum energy paths for reactions to occur, in vacuum as well as in various media. Using that, we have selected certain criteria and revealed a few metal nitride surfaces that should be efficient and selective catalysts for nitrogen reduction in water. Recently, experimental confirmation was acquired for one of the surfaces. A novel methodology was developed where electrochemical catalysis chamber was directly connected in-line with a flow injection analysis method, providing direct detection of reaction rate and catalyst current efficiency, which is then further confirmed with isotope labelling. Aiming to optimize our catalysts in the following years, we have founded Atmonia ltd. for developing the process and business model. Continue reading →

Kangyong Lee*, SeungJin Jeong, WooChul Jung, Joongmyeon Bae, Korea Advanced Institute of Science and Technology (KAIST), South Korea; Sai Katikaneni, Saudi Aramco, Saudi Arabia

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Ammonia has become one of the most important chemicals with its versatility since the Haber-Bosch process was invented. Recently, ammonia has been getting interests because of its possibility as a hydrogen carrier. Since ammonia has high energy density and carbon-free characteristics, using ammonia as a fuel of solid oxide fuel cells is advantageous. However, the Haber-Bosch process spends much electricity because of the high pressure condition, and the process consumes more than 1% of energy consumption worldwide. Therefore, the development of a new method for the ammonia production is necessary.

In this study, solid oxide based electrolytic cells were fabricated to synthesize ammonia in an electrochemical way. Various metal catalysts were tested with the electrolytic cells to synthesize ammonia, and an infiltration method was introduced to enlarge triple-phase boundaries of the cells. Operating temperatures and bias were also varied to find the feasible condition for the electrochemical ammonia synthesis. The production rate was compared to the previously reported values, and it is over 1×10-9 mol NH3∙s∙cm-2. Also, to see the feasibility of the ammonia operation of the fuel cells, the performance of solid oxide fuel cells was tested under ammonia-fed condition and compared to hydrogen-fed condition. At the single-cell level, the performance under the ammonia-fed condition showed about 20% difference compared to the hydrogen-fed condition. Continue reading →

Victoria Smith, Aditya Prajapati*, Meenesh R. Singh, University of Illinois at Chicago, USA

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

The ability to produce ammonia in a sustainable and efficient manner has been a topic of scientific and industrial importance for many years. The Haber-Bosch process has acted as the primary process for transforming nitrogen and hydrogen gas into ammonia. This process has become unsustainable in the foreseeable future and requires a cost-effective alternative. Ammonia is a critical component of fertilizer that is vital to the agriculture industry. The electrochemical reduction of N2 to ammonia would eliminate carbon dioxide emissions that are present in current ammonia production processes and allow for a environmentally favorable process. Although the electrochemical reduction of nitrogen to ammonia has been researched as an alternative process, the high temperature and pressure requirements have not allowed for the advancement of the field. This project further investigates the potential for electrochemical reduction of nitrogen to ammonia via transition metal electrocatalysts. The challenge is to develop not only an active, but selective catalyst for ammonia production. We utilized a compact, parallel plate electrochemical cell that allowed for the study of transition metal activity for electrochemical reduction of nitrogen at ambient temperature and pressure. The product distribution resulting from the electrochemical reduction of nitrogen and the corresponding Faradaic efficiencies have been reported for first and second row transition metals. Moreover, several operating conditions were tested and electrocatalytic stability was monitored. Continue reading →

Alex Schechter*, Revanasiddappa Manjunatha, Ariel University, Israel

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Ammonia was electrochemically produced from nitrogen and water using a ruthenium–platinum (RuPt) alloy catalyst cathode and a nickel anode at ambient pressure and room temperature. The rate of ammonia formation was 5.1 × 10⁻⁹ gNH3 s⁻¹ cm⁻² with a 13.2% faradaic efficiency at an applied potential of 0.123 V vs. RHE; it reached 1.08 × 10⁻⁸ gNH3 s⁻¹ cm⁻² at 0.023 V. Ammonia production was investigated under selected potentials and temperatures. Real-time direct electrochemical mass spectrometric (DEMS) analysis of the evolved gases was performed at various applied potentials. In general, the mass-to-charge ratio signals of hydrogen and ammonia were detected, and their intensities increased with increasing potentials; however, there was no trace of a hydrazine signal. Compared to metallic ruthenium and platinum catalysts, RuPt showed a synergistic effect toward electrochemical formation of ammonia due to co-catalysis. Continue reading →

Charles Loney*, Julie N. Renner, Case Western Reserve University, USA; David Suttmiller, Lauren F. Greenlee, University of Arkansas, USA; Michael Janik, Pennsylvania State University, USA

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Approximately half of the people on the planet are alive because of synthetically produced ammonia. However, due to the fossil fuels used in the current ammonia synthesis process, its production contributes a significant amount to the world’s greenhouse gas emissions. Haber-Bosch synthesis, which is the most widely used method of producing synthetic ammonia today, requires high temperatures (400-500 °C) and pressures (150-200 atm). This process is also energy intensive, consuming approximately 2% of worldwide energy. By taking an electrochemically-based approach to ammonia synthesis, those harsh conditions and emissions can be eliminated. However, current catalysts are not selective for the desired reaction.

We hypothesize that 3D surface modifications can be utilized to overcome these selective limitations and create catalysts which mimic the selectivity of the nitrogenase enzyme: an enzyme that catalyzes the reduction of nitrogen to ammonia at mild temperatures and pressures. Therefore, in this study, we show that a peptide sequence, when bound to iron (iii) oxide metal nanoparticles, facilitates electrochemical ammonia with relatively high efficiency. These recent results were obtained in an alkaline, solid-state electrochemical cell, yielding an electrochemical ammonia production rate and faradaic efficiency that is >10x higher than the catalyst without bound peptide. These results are corroborated in an alkaline liquid-based cell. Continue reading →

Sharad Maheshwari*, Yawei Li, Michael Janik, Pennsylvania State University, USA; Gholamreza Rostamikia, University of North Carolina, USA; Lauren F. Greenlee, University of Arkansas, USA; Julie N. Renner, Case Western Reserve University, USA

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Ammonia is currently produced through the catalytic Haber Bosch process (HB) at temperatures of about 300 to 500 °C and pressure of about 200-300 atm. In a future with plentiful renewable electricity from distributed sources, an electro-chemical system to produce ammonia could efficiently generate ammonia on site and on demand. Possible heterogeneous catalysts for electro-chemical nitrogen reduction are currently marred by the poor rate and selectivity due to difficulty in activating the strong N-N bond and to the competing hydrogen evolution reaction (HER), resulting in infeasible faradaic efficiency. To develop more selective and active catalysts, better understanding of the mechanistic and kinetic aspects of nitrogen electro-reduction is essential. We use density functional theory (DFT) methods to examine the elementary kinetics of the possible associative mechanisms for electro-reduction of N2. A comprehensive electro-reduction mechanism with elementary activation barriers for each step will be presented on iron (Fe) surfaces. Key step barriers are also evaluated across a series of late transition metal catalysts to evaluate the reliability of scaling and Bronsted-Evans-Polanyi relationships to predict catalyst performance. We compare the “kinetic over-potential” to the thermodynamic over potential to emphasize the need to explicitly evaluate barriers in predicting catalyst performance. We then examine how near-surface additives can act as shuttling agents to alter the kinetic barriers of the proton coupled electron transfer, acting as co-catalysts to improve activity and selectivity. Continue reading →

Xuan Yang*, Jared Nash, Jacob Anibal, Marco Dunwell, Yushan Yan, Bingjun Xu, University of Delaware, USA

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

Transition metal nitride nanoparticles are synthesized and utilized as catalysts for electrochemical nitrogen reduction reaction (ENRR) to produce ammonia in a proton exchange membrane electrolyzer (PEMEL). The catalysts show an average ENRR rate and Faradaic efficiency (FE) of 3.3 × 10⁻¹⁰ mol s⁻¹ cm⁻² (6.6 × 10⁻¹⁰ mol s⁻¹ mg⁻¹) and 5.95% at −0.1 V within 1 h, respectively. Both the ENRR rate and FE are approximately two orders of magnitude higher than those of noble metal catalysts. Time-dependent results suggest that the catalytic activity of transition metal nitride nanoparticles is stable at −0.1 V, with the catalytic activity decreasing by only 28% during 4 h test. Ex situ X-ray photoelectron spectroscopy (XPS) and operando electrochemical and synchrotron-based X-ray absorption spectroscopic (XAS) analysis reveal that transition metal oxynitride is the active phase for nitrogen reduction. Continue reading →

Jared Nash*, Xuan Yang, Jacob Anibal, Yushan Yan, Bingjun Xu, University of Delaware, USA

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

With the development of the Haber process and the subsequent work done by Bosch, ammonia production become an industrially and economically viable way to fix nitrogen. This helped increase the global population and estimates put it at about 40% of the global population’s food comes from ammonia made by the Haber-Bosch process[1]. However, the Haber-Bosch process is an energy intensive process requiring high pressure (15-30 MPa) and relatively high temperature (430 °C – 480 °C) and is highly centralized with only about 13 companies and about 29 plants[2,3]. Renewable energy resources offer a possible alternative way to fix nitrogen at low temperature and low pressure to produce ammonia in a decentralized way. High temperature solid proton conductors have been used to produce ammonia selectively, but the high temperature can degrade the ammonia[5] and the required heating makes distributed production difficult. Low temperature polymer electrolyte membranes can be used which might reduce the overall energy input. The most prevalent polymer electrolyte is an acidic proton exchange membrane (PEM). Platinum group metals (PGMs) are the standard option for electrochemical testing, especially in PEM setups. However, they generally have low Faradaic efficiencies (FE) of less than 1% toward the electrochemical nitrogen reduction reaction (ENRR) with the rest going toward the hydrogen evolution reaction (HER). We examined other non-PGM catalysts for ammonia production, focusing on metal nitrides because metal nitrides have been predicted, computationally, to be more effective catalysts for ENRR, however, experimental verification has been lacking. We previously have shown that a transition metal nitride (Cr2N) is an active and stable ENRR catalyst in a PEM electrolyzers. In this work, we compare the activity of a variety of monometallic metal nitrides, and demonstrate how the composition of mixed metal nitrides, specifically chromium nitride and vanadium nitride, affects the overall ENRR stability and activity. Continue reading →