Scheme 1. Schematic view of green and sustainable energy landscape based on electrocatalysis, where eCO2RR, RANC, and oxygen electrochemistry (OER and ORR) are highlighted in green, blue and red, respectively.

Fig. 1. (a) Local atomic structures of IS, TS, and FS for monolayer and multilayer (i) models. The light blue, blue, red, and white atoms are Ag, N, O, and H, respectively. The green atom is the transferred proton. (b) Extrapolated electrochemical barriers plotted against work function (Φ) for Volmer and NO protonation reactions using monolayer and multilayer water structures on Ag(111). Reprinted with permission from Ref. [45]. Copyright 2021, American Chemical Society.

Fig. 2. Free energy diagrams for eNORR to NH3 (a) and HER (b) at low potentials, where the subfigures show the potential-dependent barriers of corresponding potential-determining steps (PDSs), calculated with a monolayer (circle) and multilayer (triangle) water structure. Theoretical (c) and experimental (d) Faradaic efficiencies of different products on Ag. Reprinted with permission from Ref. [45]. Copyright 2021, American Chemical Society.

Fig. 3. (a,b) Calculated charge transfer (Δq, the surface charge of final states was set as reference to be 0) and work function (Φ) on the surfaces at IS, TS and FS for electrochemical processes in OER, including reaction of O* coupling with deprotonated H2O (a) and OOH* deprotonation step (b). (c) Free energy diagram, with potential-dependent activation barriers for each elementary step, for OER over Co2MnO4 at 1.23 and 1.70 V vs. RHE. (d) Comparison between the experimental current (log(j)) and theoretical rate (log(TOF)) calculated by microkinetic modelling on Co2MnO4 at various electrode potentials. Reprinted with permission from Ref. [48]. Copyright 2021, Springer Nature.

Fig. 4. (a) The scheme of potential-dependent β and reaction energy diagrams for a proton-electron coupled transfer step (A* + (H+ + e-) → AH*) at different potential in subFig.s, where the atomic models schematically show the IS-like and FS-like transition states. (b) Schematic charge transfer (Δq) and work function (Φ) on the surfaces at IS, TS and FS for A* + (H+ + e-) → AH* step. Note that Δq and Φ of TS will alter between FS and IS along coordinates of work function.

Fig. 5. (a) The one-dimensional reaction phase diagram (RPD) for CO2RR, where the solid lines show the GRPD-limiting steps for the more favored COOH* path (red) and the HCOO* path (blue). (b) Comparison between the theoretical descriptor of activity (-GRPD-limiting) and the experimental activity (log[-j(A?cm-2)]). The dashed line shows the correlation between experimental and theoretical activity, which is described by the GRPD-limiting energy of the more favored path through either COOH* or HCOO*. Reprinted with permission from Ref. [56]. Copyright 2021, Springer Nature.

Fig. 6. (a-c) Comparison of potential-turnover frequency (TOF) from microkinetic modelling between electrochemical (blue) and thermochemical (black) steps in O2* (a), OOH* (b) and O* (c) conversion. (d) Theoretical activity (log(i)) based on microkinetic modeling with the fitted Tafel slopes at the high and low electrode potential based on the experiments (insert Figure). (e) GRPD-limiting steps for two-dimensional RPD with the descriptor of EadO* and EadOH* at 0.5 V vs. RHE displayed in different colors with the color bar on the right. The reactions from R1 to R8 are O2(g) + * ↔ O2*, O2* + * ↔ 2O*, OOH* + * ↔ OH* +O*, H2O(l) + O* + * ↔ 2OH*, O* + (H+ + e-) ↔ OH*, OH* + (H+ + e-) ↔ H2O(l) + *, O2* + (H+ + e-) ↔ OOH* and OOH* + (H+ + e-) ↔ H2O(l) + O*. (Potential-dependent two-dimensional RPDs at different electrode potentials of 0.5 V (f), 0.7 V (g), and 0.9 V (h) vs. RHE. The peak of the GRPD activity trend at different electrode potentials was showed as a triangle (0.5 V), circle (0.7 V), and square (0.9 V). The GRPD were showed relevant to the color bar on the right. The data was adopted with permission from Ref. [59]. Copyright 2020, American Chemical Society.

Fig. 7. Competition between N2O and NH3 production in eNORR, at high potentials. (a) Degree of rate control of different elementary steps (XRC) for N2O production. (b) Theoretical reaction rate for N2O and NH3 production, where “n” is the electron transfer number for corresponding total reactions. The inset Fig. shows the partial current densities (jpar) from experiment, obtained with the equation jpar = jtot × FE, where “jtot” is the total current density. Reprinted with permission from Ref. [45]. Copyright 2021, American Chemical Society.

Fig. 8. Calculated charge transfer (Δq) and potential variation at IS and TS with respect to FS of Volmer (a) and Heyrovsky (b) steps in HER; Calculated potential-dependent forward reaction energies (ΔE), forward kinetic barriers (Ea), and backward kinetic barriers (Eb) on Cu(211) surface for Volmer (c) and Heyrovsky (d) reactions, in confined nanoscale reactors. (e) Micro-kinetic modeling of HER with the Volmer and Heyrovsky path. The pink and blue lines are the TOFs of reactions on the open Cu(211) and Cu(211) with graphene cover, respectively. (f) Scheme of confinement energy (Econ) formation, resulting in more favorable reaction energies and lower electrochemical kinetic barrier. Econ is defined as the difference between an open system (red dots) and the confined electrochemical system (blue dots), which is composed of two components including the enhanced (electro)chemical potential of the proton and weakening the adsorption energies of adsorbates. Reprinted with permission from Ref. [63]. Copyright 2019, American Chemical Society.