Table S8.

Corrected free-energy barriers (ΔG^‡, in electronvolts) and corrected free-energy differences (ΔG, in electronvolts) for various reduction steps of C₂H₄ formation on Cu(100) at pH 7 and 298 K

ID	Reaction equation	ΔG‡, eV	ΔG, eV
0	$\text{*CO}+\text{*CO}+\mathrm{\delta }\cdot e^{-}\to {\text{*CO–CO}}^{\mathrm{\delta -}}$	0.69	0.56
1	${\text{*OC–CO}}^{\mathrm{\delta -}}+{\text{H}}_2\text{O}+\left(1-\mathrm{\delta }\right)\mathrm{\cdot }{\text{e}}^{-}\to \text{*CO–COH}+{\text{OH}}^{-}$	0.14	−0.01
2	$\text{*CO–COH}+{\text{H}}_2\text{O}+e^{-}\to \text{*COH–COH}+{\text{OH}}^{-}$	0.02	−0.17
2a	${\text{*OC–CO}}^{\mathrm{\delta -}}+\text{H*}\to {\text{*CHO–CO}}^{\mathrm{\delta -}}$	1.12	0.55
3	$\text{*COH–COH}+e^{-}\stackrel{{\text{H}}_2\text{O}}{\to }\text{*C–COH}+{\text{OH}}^{-}$	0.62	0.38
3a	$\text{*COH–COH}+\text{H*}\to \text{*CHOH–COH}$	1.06	0.80
4	$\text{*C–COH}+{\text{H}}_2\text{O}+e^{-}\to \text{*CH–COH}+{\text{OH}}^{-}$	0.44	0.17
4a	$\text{*C–COH}+\text{H*}\to \text{*CH–COH}$	0.91	−0.02
4b	$\text{*C–COH}+e^{-}\to \text{*C–C}+{\text{OH}}^{-}$	1.18	0.76
4c	$\text{*C–COH}+\text{H*}\to \text{*C–CHOH}$	1.00	0.36
5	$\text{*CH–COH}+e^{-}\stackrel{{\text{H}}_2\text{O}}{\to }\text{*C–CH}+{\text{OH}}^{-}$	0.61	−0.16
5a	$\text{*CH–COH}+\text{H*}\to {\text{*CH}}_2\text{–COH}$	1.41	1.21
5b	$\text{*CH–COH}+\text{H*}\to \text{*CH–CHOH}$	1.05	0.83
6	$\text{*C–CH}+{\text{H}}_2\text{O}+e^{-}\to {\text{*C–CH}}_2+{\text{OH}}^{-}$	0.60	0.13
6a	$\text{*C–CH}+\text{H*}\to {\text{*C–CH}}_2$	0.93	0.39
6b	$\text{*C–CH}+{\text{H}}_2\text{O}+e^{-}\to \text{*CH–CH}+{\text{OH}}^{-}$	1.07	0.79
6c	$\text{*C–CH}+\text{H*}\to \text{*CH–CH}$	1.41	0.67
7	${\text{*C–CH}}_2+{\text{H}}_2\text{O}+e^{-}\to {\text{*CH–CH}}_2+{\text{OH}}^{-}$	0.49	0.32
7a	${\text{*C–CH}}_2+\text{H*}\to {\text{*CH–CH}}_2$	1.10	0.41
7b	${\text{*C–CH}}_2+\text{H*}\to {\text{*C–CH}}_3$	1.76	1.74
8	${\text{*CH–CH}}_2+{\text{H}}_2\text{O}+e^{-}\to {\text{C}}_2{\text{H}}_4+{\text{OH}}^{-}$	0.38	−0.14
8a	${\text{*CH–CH}}_2+\text{H*}\to {\text{C}}_2{\text{H}}_4$	1.15	0.01
8b	${\text{*CH–CH}}_2+{\text{H}}_2\text{O}+e^{-}\to {\text{*CH–CH}}_3+{\text{OH}}^{-}$	0.68	0.63
8c	${\text{*CH–CH}}_2+\text{H*}\to {\text{*CH–CH}}_3$	1.21	0.56

The work functions are referenced to the initial states.