An official website of the United States government
Abstract A glut of dinitrogen‐derived ammonia (NH3) over the past century has resulted in a heavily imbalanced nitrogen cycle and consequently, the large‐scale accumulation of reactive nitrogen such as nitrates in our ecosystems has led to detrimental environmental issues. Electrocatalytic upcycling of waste nitrogen back into NH3holds promise in mitigating these environmental impacts and reducing reliance on the energy‐intensive Haber–Bosch process. Herein, we report a high‐performance electrolyzer using an ultrahigh alkalinity electrolyte, NaOH−KOH−H2O, for low‐cost NH3electrosynthesis. At 3,000 mA/cm2, the device with a Fe−Cu−Ni ternary catalyst achieves an unprecedented faradaic efficiency (FE) of 92.5±1.5 % under a low cell voltage of 3.83 V; whereas at 1,000 mA/cm2, an FE of 96.5±4.8 % under a cell voltage of only 2.40 V was achieved. Techno‐economic analysis revealed that our device cuts the levelized cost of ammonia electrosynthesis by ~40 % ($30.68 for Fe−Cu−Ni vs. $48.53 for Ni foam per kmol‐NH3). The NaOH−KOH−H2O electrolyte together with the Fe−Cu−Ni ternary catalyst can enable the high‐throughput nitrate‐to‐ammonia applications for affordable and scalable real‐world wastewater treatments.
more »
« less
High‐Performance Ammonia Electrosynthesis from Nitrate in a NaOH−KOH−H 2 O Ternary Electrolyte
Abstract A glut of dinitrogen‐derived ammonia (NH3) over the past century has resulted in a heavily imbalanced nitrogen cycle and consequently, the large‐scale accumulation of reactive nitrogen such as nitrates in our ecosystems has led to detrimental environmental issues. Electrocatalytic upcycling of waste nitrogen back into NH3holds promise in mitigating these environmental impacts and reducing reliance on the energy‐intensive Haber–Bosch process. Herein, we report a high‐performance electrolyzer using an ultrahigh alkalinity electrolyte, NaOH−KOH−H2O, for low‐cost NH3electrosynthesis. At 3,000 mA/cm2, the device with a Fe−Cu−Ni ternary catalyst achieves an unprecedented faradaic efficiency (FE) of 92.5±1.5 % under a low cell voltage of 3.83 V; whereas at 1,000 mA/cm2, an FE of 96.5±4.8 % under a cell voltage of only 2.40 V was achieved. Techno‐economic analysis revealed that our device cuts the levelized cost of ammonia electrosynthesis by ~40 % ($30.68 for Fe−Cu−Ni vs. $48.53 for Ni foam per kmol‐NH3). The NaOH−KOH−H2O electrolyte together with the Fe−Cu−Ni ternary catalyst can enable the high‐throughput nitrate‐to‐ammonia applications for affordable and scalable real‐world wastewater treatments.
more »
« less
- Award ID(s):
- 2219172
- PAR ID:
- 10507870
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 22
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Ammonia (NH3) electrosynthesis gains significant attention as NH3is essentially important for fertilizer production and fuel utilization. However, electrochemical nitrogen reduction reaction (NRR) remains a great challenge because of low activity and poor selectivity. Herein, a new class of atomically dispersed Ni site electrocatalyst is reported, which exhibits the optimal NH3yield of 115 µg cm−2h−1at –0.8 V versus reversible hydrogen electrode (RHE) under neutral conditions. High faradic efficiency of 21 ± 1.9% is achieved at ‐0.2 V versus RHE under alkaline conditions, although the ammonia yield is lower. The Ni sites are stabilized with nitrogen, which is verified by advanced X‐ray absorption spectroscopy and electron microscopy. Density functional theory calculations provide insightful understanding on the possible structure of active sites, relevant reaction pathways, and confirm that the Ni‐N3sites are responsible for the experimentally observed activity and selectivity. Extensive controls strongly suggest that the atomically dispersed NiN3site‐rich catalyst provides more intrinsically active sites than those in N‐doped carbon, instead of possible environmental contamination. This work further indicates that single‐metal site catalysts with optimal nitrogen coordination is very promising for NRR and indeed improves the scaling relationship of transition metals.more » « less
-
Abstract Aldehyde‐assisted water electrolysis offers an attractive pathway for energy‐saving bipolar hydrogen production with combined faradaic efficiency (FE) of 200% while converting formaldehyde into value‐added formate. Herein we report the design and synthesis of noble metal‐free Cu6Sn5alloy as a highly effective electrocatalyst for formaldehyde electro‐oxidative dehydrogenation, demonstrating a geometric current density of 915 ± 46 mA cm−2at 0.4 V versus reversible hydrogen electrode, outperforming many noble metal electrocatalysts reported previously. The formaldehyde‐assisted water electrolyzer delivers 100 mA cm−2at a low cell voltage of 0.124 V, and a current density of 486 ± 20 mA cm−2at a cell voltage of 0.6 V without any iR compensation and exhibits nearly 200% faradaic efficiency for bipolar hydrogen production at 100 mA cm−2in 88 h long‐term operation. Density functional theory calculations further confirm the notably lowered barriers for dehydrogenation and Tafel steps on the Cu₆Sn₅ surface compared to Cu, underscoring its potential as a highly active catalyst.more » « less
-
Abstract The electrochemical reduction of nitrates (NO3−) enables a pathway for the carbon neutral synthesis of ammonia (NH3), via the nitrate reduction reaction (NO3RR), which has been demonstrated at high selectivity. However, to make NH3synthesis cost‐competitive with current technologies, high NH3partial current densities (jNH3) must be achieved to reduce the levelized cost of NH3. Here, the high NO3RR activity of Fe‐based materials is leveraged to synthesize a novel active particle‐active support system with Fe2O3nanoparticles supported on atomically dispersed Fe–N–C. The optimized 3×Fe2O3/Fe–N–C catalyst demonstrates an ultrahigh NO3RR activity, reaching a maximum jNH3of 1.95 A cm−2at a Faradaic efficiency (FE) for NH3of 100% and an NH3yield rate over 9 mmol hr−1cm−2. Operando XANES and post‐mortem XPS reveal the importance of a pre‐reduction activation step, reducing the surface Fe2O3(Fe3+) to highly active Fe0sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe2O3particles and Fe–Nxsites at highly cathodic potentials, maintaining a current of −1.3 A cm−2over 24 hours. This work exhibits an effective and durable active particle‐active support system enhancing the performance of the NO3RR, enabling industrially relevant current densities and near 100% selectivity.more » « less
-
Abstract The broad employment of water electrolysis for hydrogen (H2) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a Cu3Ag7electrocatalyst. Such a strategy not only produces more valuable anodic product than O2but also releases H2at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(–) can produce H2at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2with a cell voltage of only 0.60 V.more » « less
