Table 9.

Catalytic systems, major products, maximum FEs, and mechanisms of Ni complexes in electrochemical CO₂ reduction (n.a.=not available, prop.=proposal, comp.=computational investigation, exp.=experimental evidence).

Entry	Cat. system	Substitution	Major product	Max. FE (%)	Mechanism	Basis	Method	Ref.
1		R= –, H	CO/H2O	44 [241a]	ETH	prop. [241a]	n.a.	[ 241a , 290 ]
2a		R1=H, Me; R2=H, propyl, Bn, (CH2)2OH, CO2H, NH2, R3=H, Me2, Ph, tolyl, C6H4CF3 R4=R5=H, Me, Me2 R4∩R5=Cy Y=NH, NMe Z=CH, N	CO/H2O HCO2 − H2	99 [283] 75 [54a] 53 [296]	ETM (CO) ETH (HCO2H)	exp. comp. [297]	IR‐SEC, [292] PR[ 284 , 298 ] DFT	[54a, 62b, 241, 283, 284, 287, 291, 292, 296–299]
2b			CO/H2O H2	54 89	n.a.	n.a.	n.a.	[300]
2c		n=0, 2 (C6H4‐bridged), 3, 4, 6 R=H, Me Y=CH, N	CO/H2O HCO2 −	95 [299g] 68 [54a]	ETM (CO) ETH (HCO2H)	prop. [54a] comp. [299g]	n.a. DFT	[ 54a , 299e , 299g ]
2d		–	CO/H2O H2	79 (com‐ bined)	ETM	prop.	n.a.	[301]
2e		R1=Me, Ph R2=H, COMe, CO2Et Y=(CH2)2, (CH2)3	C2O4 2−	98	ETM	prop.	n.a.	[294]
2f		–	C2O4 2−	n.a.	ETM	exp.	IL, IR, UV/Vis	[54b]
2g		–	CO/H2O	95	n. a	n.a.	n.a.	[ 299e , 302 ]
2h		–	CO/H2O	96	n.a.	n.a.	n. a	[302]
3a		n=0, 1, 2 R=Me, Bu X=MeCN, Cl Y=C, N	CO/H2O HCO2 −	34 [303] 47 [303]	ETM [304]	exp. comp.	UV/Vis DFT	[ 303 , 304 , 305 ]
3b		–	CO/H2O H2	25 55	ETM (CO) ETH (H2)	exp. comp.	IR‐SEC DFT	[306]
4a		R=Me, Bu, 2,6‐Me2C6H3	CO/CO3 2−	n.a.	ETM	exp.	IL, IR‐SEC	[307]
4b		L=CO, MeCN, iPrCN, tBuCN, C6H11CN, CH2C6H5CN, 2,6‐Me2C6H3CN	CO/CO3 2−	n.a.	ETM	prop.	n.a.	[308]
5		R=H, CO2H, PO3H2, SH	CO/CO3 2− H2	43 [309] 67 [309]	ETM	exp. [309]	IR‐SEC, UV/Vis	[ 254 , 309 ]
6a		–	CO/H2O	61	n.a.	n.a.	n.a.	[310]
6b		–	CO/H2O	82	n.a.	n.a.	n.a.	[310]
7		R=H, NH2	HCO2H MeOH C2H5OH CH3CHO H2	11 16 36 7 65	ETM	prop.	n.a.	[295]
8		R1= –, Me R2= –, Ac	HCO2 −	70 [311]	ETH	comp. [312]	DFT	[ 311 , 312 ]
9	[Ni(TPEN)]2+	TPEN=N,N,N′,N′‐tetrakis(2‐pyridylmethyl) ethylenediamine	CO/CO3 2− CO/H2O	n.a.	ETM	comp.	DFT	[313]
10		Y=Me Y∩Y=CH2, (CH2)2	CO/H2O H2	87 93	ETM (CO) ETH (H2)	comp.	DFT	[314]
11		–	CO/CO3 2− CH4 H2	23±2[a] (combined)	ETM (CO)	exp. comp.	IR‐SEC DFT	[315]

[a] Degradation of the catalyst to Ni(CO) species