“…The attention on non-noble metal-based SACs has grown rapidly since 2018. Their applications have been extended to non-oxidative CH 4 conversion using Fe 1 /SiO 2 [61]; HER with Co 1 on N-doped graphene [59], graphitic carbon nitride [62], N-doped graphyne [63], and Ni 1 on α-SiX (X = N, P, As, Sb, Bi) [64]; ethylene benzene oxidation using Co 1 /CN [65]; electrocatalytic ethanol oxidation using a hybrid material of Pd nanoparticles and Ni 1 single atom [66]; oxidative desulphurization with Cr 1 /multiwalled carbon nanotubes [67]; CO oxidation using Ni 1 over FeO x [68], phosphorene nanosheet [69], Sc 1 and Fe 1 on honeycomb borophene/Al (111) heterostructure [70], and Ti 1 on MXene [71]; acetylene hydration using Zn 1 with S/N co-doped defective graphene supports [72]; the electrochemical CO 2 RR with Ni 1 on N-doped porous carbon [73], graphene nanosheets [74], carbon black [75] and other ZnN 4 -based SACs [76]; CO 2 hydrogenation with various non-noble metal-based SAC (Mn 1 , Fe 1 , Co 1 , Mo 1 ) supported on graphitic carbon nitride [77]; ORR has been carried out with Co 1 on defective N-doped carbon graphene [78], Fe 1 supported on N-doped porous carbon [79], hierarchically structured porous carbon [80], cellulose-derived nanocarbon [81] and phosphomolybdic acid cluster [82]; and the Oxygen Evolution Reaction (OER) has been carried out on Fe, Co and Ni-based SACs on N-doped graphene [83], N-doped biomass-derived porous carbon [84] as well as γ-graphyne monolayer [85]. Lastly, the production of H 2 O 2 was found to be effective via hydrogenation routes Ni-based SACs [86].…”