Recent Advances in Electrocatalytic Nitrate Reduction to Ammonia Using Metal Oxides

doi:10.15541/jim20240102

Abstract

Abstract:

Ammonia serves not only as a primary raw material in synthetic fertilizers, but also as a novel high-energy- density fuel. In recent years, electrocatalytic nitrate reduction for ammonia synthesis has gained extensive attention as a green and sustainable approach due to its potential as an eco-friendly and sustainable way that could replace the energy-intensive and high-carbon-emission Haber-Bosch process. Nevertheless, the efficient electrocatalytic ammonia synthesis is still hampered by low reaction efficiency and product selectivity as well as catalyst stability. Hence, there is a pressing need to develop efficient catalysts to advance electrocatalytic nitrate reduction for ammonia synthesis. Recently, metal oxide catalysts have been at the center of attention for their superior performance in electrocatalytic nitrate reduction for ammonia synthesis. This review consolidates the developments of metal oxide electrocatalysts converting nitrate to ammonia, focusing on elucidating the reaction mechanism and introducing typical metal-based (Cu, Fe, Ti, etc.) catalysts. Additionally, it discusses the latest research progress in enhancing catalytic reaction efficiency, product selectivity, and material stability through strategies like morphology control, surface reconstruction, oxygen vacancy engineering, element doping, metal-assisted catalyst loading, etc. Finally, the paper outlines the challenges and future research directions in the realm of electrocatalytic nitrate reduction for ammonia synthesis.

Key words: electrocatalysis, nitrate reduction to ammonia, metal oxide, modulation strategy, review

CLC Number:

TQ113
TQ13

YANG Xin, HAN Chunqiu, CAO Yuehan, HE Zhen, ZHOU Ying. Recent Advances in Electrocatalytic Nitrate Reduction to Ammonia Using Metal Oxides[J]. Journal of Inorganic Materials, 2024, 39(9): 979-991.

Figures/Tables 9

Fig. 1 Main process of electrocatalytic production for N2/NH3

Table 1 Properties of metal oxides used in the study of eNitRR

Catalyst	NH₃ yield rate	Faraday efficiency, FE/%	Stability/h	Ref.
TiO_2-_x	45.00 µmol·h^-1·mg^-1	85.00	16.00	[40]
Ru/TiO₂	35.35 µmol·h^-1·cm^-2	>90.00	4.50	[41]
Pd/TiO₂	66.00 μmol·h^-1·cm^-2	92.00	12.00	[42]
PdCu/TiO_2-_x	322.70 μmol·h^-1·cm^-2	80.10	48.00	[43]
Co-TiO₂/TP	1127.00 μmol·h^-1·cm^-2	98.20	24.00	[44]
Fe₂TiO₅	0.73 mmol·h^-1·mg^-1	87.60	6.00	[45]
ZnCr₂O₄	1197.65 μmol·h^-1·mg^-1	90.20	15.00	[46]
Fe₂O₃	328.17 μmol·h^-1·cm^-2	69.80	5.00	[47]
Fe₃O₄/SS	596.76 μmol·h^-1·cm^-2	91.50	4.00	[48]
Cu/Fe₃O₄	10.56 mmol·h^-1·mg^-1	100.0	-	[49]
NiO₄	1.83 mmol·h^-1·mg^-1	94.70	72.00	[32]
Co₃O₄/NiO	6.93 μmol·h^-1·mg^-1	-	3.00	[50]
Cu/Cu₂O	219.80 μmol·h^-1·cm^-2	93.90	12.00	[51]
Cu₂O	0.14 mmol·h^-1·cm^-2	99.80	20.00	[52]
PdCu/Cu₂O	190.00 μmol·h^-1·cm^-2	94.30	12.00	[28]
CoO NC/graphene	25.63 mmol·h^-1·mg^-1	>98.00	6.00	[53]
Cu/Co₃O₄	1.11 mmol·h^-1·cm^-2	100.70	60.00	[54]
S/Co₃O₄	174.20 μmol·h^-1·mg^-1	89.90	7.00	[55]
Cu/MnO_x	1.72 mmol·h^-1·mg^-1	86.20	6.00	[56]
CuO@MnO₂/CF	0.24 mmol·h^-1·cm^-2	94.90	10.00	[57]

Fig. 2 Metal oxides for selective regulation of eNitRR

Fig. 3 Catalytic performance of Cu/Cu2O NWAs[63] (a) Nitrate conversion efficiency and FE at different voltages; (b) Nuclear magnetic resonance (NMR) spectra of nitrogen sources; (c) Raman spectra; (d) In-situ mass spectrometry spectra; (e) Free energy image

Fig. 4 Characterization of catalytic performance of Cu/Cu2O[51] (a) FE of NH3 and NO2− at different potentials; (b) Corresponding NH3 generation rates and bias current densities at different potentials; (c) Potential-induced electrocatalytic reconstruction of Cu2O cube; (d) Free energy diagram

Fig. 5 Characterization of catalytic performance of Fe3O4/SS[48] (a) Current density of different product fractions; (b) Ammonia-producing activity of Fe3O4/SS; (c) Cyclic test of Fe3O4/SS at -0.50 V; (d) Free energy diagram

Fig. 6 Characterization of catalytic performance of Cu-Fe3O4[49] (a) NH3 yield and FE of Cu-Fe3O4; (b) Comparison of ammonia yields of different catalytic materials; (c) Free energy diagram

Fig. 7 Characterization of catalytic performance of TiO2-x[40] (a) NO3- conversion rates and NH3 FE of TiO2-x; (b) TiO2-x ammonia production cycle test; (c) Differential electrocatalytic mass spectra; (d, e) Free energy diagrams of (d) TiO2 and (e) TiO2-x

Fig. 8 Characterization of catalytic performance of PdCu NPs/TiO2-x[43] (a) Ammonia production activity and FE of different materials; (b) Product selectivity of different materials; (c, d) Partial crystal orbital layouts of (c) TiO2-x and (d) PdCu NPs/TiO2-x; (e) Density of states diagram; (f) Schematic diagram of catalytic kinetics of the d band center

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