Experimental results have shown that CO2 electroreduction is sensitive to the surface morphology of Cu electrodes. We used density functional theory (DFT) to evaluate the thermodynamics and kinetics of CO2 reduction pathways on Cu(100) and Cu(111) with the aim of understanding the experimentally reported differences in CO2 reduction products. Results suggest that the hydrogenation of CO* to hydroxymethylidyne (COH*) or formyl (CHO*) is a key selective step. Cu(111) favors COH* formation, through which methane and ethylene are produced via a common CH2 species under high overpotential (<−0.8 V vs RHE). On Cu(100), formation of CHO* is preferred and ethylene formation goes through C–C coupling of two CHO* species followed by a series of reduction steps of the C2 intermediates, under relatively lower overpotential (−0.4 to −0.6 V vs RHE). Further reduction of these C2 intermediates, however, require larger potentials (∼−1.0 V vs RHE) and conflicts with the experimentally observed low potential pathway to C2 products on Cu(100). Calculations show that the presence of (111) step sites on the flat (100) terrace can reduce the overpotential for C2 production on the Cu electrode, which may be present on Cu(100) due to reconstruction. On Cu(100), a change in CO* coverage from low to high with increasing negative applied potential can trigger a switch from ethylene/ethanol to methane/ethylene as the reduction products by affecting the relative stability of CHO* and COH*.

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Proton reduction is one of the most fundamental and important reactions in nature. MoS2 edges have been identified as the active sites for hydrogen evolution reaction (HER) electrocatalysis. Designing molecular mimics of MoS2 edge sites is an attractive strategy to understand the underlying catalytic mechanism of different edge sites and improve their activities. Herein we report a dimeric molecular analogue [Mo2 S12 ](2-) , as the smallest unit possessing both the terminal and bridging disulfide ligands. Our electrochemical tests show that [Mo2 S12 ](2-) is a superior heterogeneous HER catalyst under acidic conditions. Computations suggest that the bridging disulfide ligand of [Mo2 S12 ](2-) exhibits a hydrogen adsorption free energy near zero (-0.05 eV). This work helps shed light on the rational design of HER catalysts and biomimetics of hydrogen-evolving enzymes.

Density functional theory (DFT) calculations on Pd-Cu bimetallic catalysts reveal that the stepped PdCu(111) surface with coordinatively unsaturated Pd atoms exposed on the top is superior for CO 2 and H 2 activation and for CO 2 hydrogenation to methanol in comparison to the flat Cu-rich PdCu 3 (111) surface. The energetically preferred path for CO 2 to CH 3 OH over PdCu(111) proceeds through CO 2 * → HCOO* → HCOOH* → H 2 COOH* → CH 2 O* → CH 3 O* → CH 3 OH*. CO formation from CO 2 via a reverse water-gas shift (RWGS) proceeds more quickly than CH 3 OH formation in terms of kinetic calculations, in line with experimental observation. A small amount of water, which is produced in situ from both RWGS and CH 3 OH formation, can accelerate CO 2 conversion to methanol by reducing the kinetic barriers for O−H bond formation steps and enhancing the TOF. Water participation in the reaction alters the rate-limiting step according to the degree of rate control (DRC) analysis. In comparison to CO 2 , CO hydrogenation to methanol on PdCu(111) encounters higher barriers and thus is slower in kinetics. Complementary to the DFT results, CO 2 hydrogenation experiments over SiO 2 -supported bimetallic catalysts show that the Pd-Cu(0.50) that is rich in a PdCu alloy phase is more selective to methanol than the PdCu 3 -rich Pd-Cu(0.25). Moreover, advanced CH 3 OH selectivity is also evidenced on Pd-Cu(0.50) at a specific water vapor concentration (0.03 mol %), whereas that of Pd-Cu(0.25) is not comparable. The present work clearly shows that the PdCu alloy surface structure has a major effect on the reaction pathway, and the presence of water can substantially influence the kinetics in CO 2 hydrogenation to methanol.

We report a periodic density functional theory (DFT) study of the methanol steam reforming (MSR) reaction on the Co(0001) and Co(111) surfaces. Thermochemistry and activation barriers for all elementary steps of two commonly accepted mechanisms, CH2O decomposition and H2COOH formation, were calculated along with the water gas shift (WGS) reaction. The adsorption energies on Co(0001) and Co(111) are within 0.05 eV for all the MSR intermediates examined, which suggests the same catalytic activity for both surfaces. On the basis of both the thermochemistry and barriers, CH2O decomposition into CHO and CO is favored over H2COOH formation on the Co(0001) surface. The strong CO binding on Co(0001) limits its WGS activity to convert CO into CO2. Our results of the MSR and WGS pathways suggest that Co will not show high selectivity toward CO2 for MSR, which matches the limited experimental data available. A simple Langmuir equilibrium model was applied to study the surface coverages on Co. The results show that O* and OH* coverages on Co are higher than on other transition metals such as Pt, Pd, and Cu due to the facile H2O activation on the surface, and reaction steps involving O–H bond breaking and forming may be facilitated by O* and OH*. The results also suggest that Co is more susceptible than other transition metals to oxide formation under steam reforming conditions, especially under high water to alcohol ratios.