Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.


Notation in
k / cm -  HER reaction mechanism and activity evaluation.
With respect to the HER in acid electrolyte (2H + + 2e -→ H2), the general consensus of the reaction mechanism can be described as follows 1, 2 : firstly, proton in the aqueous solution receives an electron and adsorbs on the catalyst surface (H + (aq) + e -+ * → H*); Subsequently, two surface adsorbed H* can couple and desorb into H2 (2H* → H2 + 2*) following the Tafel mechanism; alternatively, H* could also directly react with proton in the solution to produce H2 (H* + H + (aq) + e -→ H2 + *) following the Heyrovsky mechanism. To evaluate the activity trend, it has been revealed that the adsorption energy of H atom (Ead H ) inherently determines the free energy of these two processes and plays a crucial role in determining the whole catalytic activity. It is generally termination for the monoclinic WO3(001) surface (see Fig. 4 and Supplementary Fig. 11).
As shown in Fig. 4a Fig. 4b and Supplementary Fig. 11). Herein, we examined two kinds of possible reconstruction configurations ( Supplementary Fig. 12). To systematically examine the binding ability of WO2.9(010) surface with the stable config_1, various possible W5c sites were checked, including the sites SN (N = 1, 2, 3) in the characteristic region and a series of reference sites distributing outside this region (denoted as RN (N = 1, 2, …, 6)), as shown in Fig. 4b and Supplementary Fig. 13. As shown in Supplementary Table 3, it is interesting that the adsorption energy on all these sites is largely enhanced relative to WO3(001), and site SN (N = 1, 2, 3) in the characteristic region as well as the reference site (R1, R2, R3) nearest to the region exhibit the strongest binding ability with the order of -0.1 eV, while the farest one (R6) from the region gives the weakest binding ability (Ead H = 0.46 eV). For example, the adsorption energy at the S3 site is calculated to be -0.19 eV, and accordingly, the free energy change of the discharge step (H + + e -→ H*) for HER at the standard condition (U = 0 V vs USHE, pH = 0) is calculated to be 0.01 eV, fulfilling the ΔGH = 0 eV requirement, and thus its high catalytic activity can be expected.
Besides the W5c site, the catalytic activity of the terminal O on WO2.9(010) were also examined.
Four kinds of one-coordinated terminated oxygen, denoted as OI, OII, OIII and OIV, respectively, are selected as demonstration ( Supplementary Fig. 12). The adsorption energies were calculated to be -0.98 eV, -0.98 eV, -0.74 eV and -0.88 eV, respectively, corresponding to ΔGH = -0.50 ~ -0.74 eV, indicating their low catalytic activity (Fig. 4c) Fig. 13). It is found that the adsorption energy were further improved by the order of only ~0.30 eV compared with clean WO2.9(010) surface (Supplementary Table 4). From Fig. 4c, one can see that the activity can remain at the high level, despite being a little lower to some extent relative to clean WO2.9(010). Therefore, it can be rationalized that WO2.9 exhibits a high and stable activity. As illustrated above, the improved H adsorption ability at the surface W5c largely contribute the high catalytic activity of WO2.9(010) relative to WO3(001).
The W5c-H bond exhibits evident covalent bond on both surfaces ( Supplementary Fig. 14), mainly ascribed to the overlapping between the W5c dZ 2 orbital and H1s orbital. Projected density of state on the d-orbital (d-PDOS) of the surface W5c on WO2.9(010) and WO3(001) were analyzed, in which a series of W5c cations on WO2.9(010) were considered and the site S1 for WO2.9(010) was taken as a demonstration. As shown in Supplementary Fig. 14, WO3(001) has an evident band