Low Temperature Thermal and Solar Heating Carbon‐Free Hydrogen Production from Ammonia Using Nickel Single Atom Catalysts

Abstract

With the intense demand for carbon neutralization, [1] green hydrogen (H 2 ) produced by renewable energy has become one of the universal concerns for human society. [2] However, due to low bulk density (0.089 kg m −3 ), which limits the application and transportation of H 2 , the future of H 2 utilization lies in high-density storage. [3] Among diverse high-density hydrogen storage mediums (e.g., CH 4 , CH 3 OH), [4] ammonia (NH 3 ) not only has the advantages of a large hydrogen storage volume density of ≈106 kg m −3 but also zero CO x (CO 2 , CO) emission during the H 2 production process, [5] which is an ideal candidate for constructing the carbon-free hydrogen system. Traditionally, H 2 production from NH 3 splitting is carried out at high temperatures of 600-850 °C, [6,7] and such high operating temperatures cause serious energy consumption and severe corrosion originating from NH 3 . To reduce the reaction temperature, scientists have developed various catalysts, among which Ir and Ru-based catalysts could drive NH 3 splitting at 300 °C with a H 2 produced rate of ≈2 mmol g −1 min −1 at 300 °C. [8] Unfortunately, the expensive and low reserves of these noble metal catalysts restrict their application. [9] Ni is the benchmark and abundant catalyst for NH 3 splitting, [10,11] exhibiting relatively high activity for NH 3 splitting among non-noble metal catalysts. [6,12] Although a series of Ni-based catalysts, e.g., NiMgAl-layered double hydroxides, [13] La and Ce doped Ni catalysts, [14] Ni/molecular sieves heterostructures, [15] Ni-based solid solutions, [16] have been investigated, the highest H 2 production rate of Ni-based catalysts is still limited in ≈4 mmol g −1 min −1 at 600 °C. [16] Therefore, investigating Ni-based catalysts active for NH 3 splitting at low temperature (300 °C) is the key to realizing industrialized NH 3 splitting. [17] Herein, we proposed a Ni single atom catalyst for NH 3 splitting for the first time. Density functional theory disclosed that the atomic Ni sites supported on CeO 2 could significantly weaken the reaction barrier of NH 3 splitting. Further, the Ni single atoms on CeO 2 nanosheets (SA Ni/CeO 2 ) were successfully synthesized, showing the unprecedented ultra-low activation temperature and the high H 2 production rate for NH 3 splitting, even exceeding most of the reported noble metal Catalytic splitting NH 3 to H 2 is one of the foundations for building a carbonfree H 2 energy system but requires NH 3 splitting catalysts that are highly active and durable at low temperatures. Although various non-noble catalysts have been designed, NH 3 splitting still operates at relatively high temperatures (600-850 °C). Herein, theoretical calculations predict that the Ni single atoms can change the bonding mode of NiN from covalent bond to ionic bond to boost the NH 3 splitting activity. Further, Ni single atoms supported on CeO 2 nanosheets (SA Ni/CeO 2 ) are synthesized by the sol-gel method, which exhibits a robust 3.544 mmol g −1 min −1 of H 2 yield speed of NH 3 splitt...

Nanostructured Materials for Photothermal Carbon Dioxide Hydrogenation: Regulating Solar Utilization and Catalytic Performance

“…Photothermal catalysis, which combines photo- and thermochemical contributions of sunlight, − has become a rapidly developing and exciting research field. ,,, In particular, photothermal CO 2 hydrogenation (CO 2 + H 2 → chemicals) provides a promising way to convert CO 2 and store green H 2 produced by renewable energy, ,− which has several advantages in comparison with other catalytic modes. Compared with thermocatalysis, the photothermal catalysis can not only mitigate the fossil energy consumption but also alter the electronic structure of the catalysts under sunlight irradiation to regulate the CO 2 reduction selectivity. ,, Although photocatalysis can convert CO 2 in the absence of H 2 (CO 2 + H 2 O → chemicals), the photothermal CO 2 hydrogenation has exclusive advantages.…”

Ambient sunlight-driven high performance chlorinated volatile organic compound oxidation by Cu0.15Mn0.15Ce0.7Ox hollow spheres

“…9,10 Among the transition metal oxides, CeO 2 has the superiority of abundant oxygen vacancies, excessive oxygen storage capability, and easy transformation between Ce 3+ and Ce 4+ , making it a potential catalyst. [11][12][13] However, pure CeO 2 tends to lose oxygen mobility and deactivate rapidly owing to the strong adsorption of chlorine matter on its surface. Thus, CuO and MnO x with good catalytic activity for the destruction of CVOCs are employed to modify CeO 2 .…”

Macroporous Carbon-Nitride-Supported Transition-Metal Single-Atom Catalysts for Photocatalytic Hydrogen Production from Ammonia Splitting

“…Green hydrogen (H 2 ) has been considered as the most promising secondary clean energy for future energy sustainability. 1 Ammonia (NH 3 ) is an attractive energy carrier with a high H 2 storage capacity (17.8% by weight) and volumetric density (121 kg H 2 m −3 at 10 bar), 2,3 making it an ideal candidate for storage and safe transportation to support on-site hydrogen production compared to other H 2 storage mediums (e.g., CH 4 , CH 3 OH). As shown in Scheme 1, the existing infrastructure for manufacturing, storing, and transporting NH 3 is well-established, 4,5 and ammonia splitting (NH 3 → 1/2N 2 + 3/2H 2 ) has zero carbon (e.g., CO 2 and CO) emission.…”

“…Green hydrogen (H 2 ) has been considered as the most promising secondary clean energy for future energy sustainability . Ammonia (NH 3 ) is an attractive energy carrier with a high H 2 storage capacity (17.8% by weight) and volumetric density (121 kg H 2 m –3 at 10 bar), , making it an ideal candidate for storage and safe transportation to support on-site hydrogen production compared to other H 2 storage mediums (e.g., CH 4 , CH 3 OH). As shown in Scheme , the existing infrastructure for manufacturing, storing, and transporting NH 3 is well-established, , and ammonia splitting (NH 3 → 1/2N 2 + 3/2H 2 ) has zero carbon (e.g., CO 2 and CO) emission. , It is recognized that the worldwide energy situation has transitioned into the “ammonia = hydrogen 2.0” era. , However, the traditional ammonia cracking process suffers from several limitations (Scheme ), including (1) high operating temperatures of 600–850 °C; (2) low energy efficiency due to the burning of NH 3 during the process; (3) severe stress corrosion cracking of steel; (4) complexity of the overall system.…”

“…Single-atom catalysts (SACs) have been proven to boost performance in photocatalytic reactions due to their unique structure and maximized metal atom utilization efficiency. , For NH 3 splitting, single-atom Ni on CeO 2 has been reported for improved NH 3 splitting performance at 300 °C . However, in-depth studies of the structure–activity relationship of single-atom sites in NH 3 splitting are rarely reported.…”