# Grain Boundary--A Route to Enhance Electrocatalytic Activity for Hydrogen Evolution Reaction
## 4 Conclusions  
In summary, via DFT simulations, we studied the HER performance of Au mediated by GBs. The active site around GBs exhibited superior HER performance with a remarkably low overpotential required, which arose from the significant enhanced capacity of binding H. The Au catalyst with GBs was experimentally prepared using the magnetron sputtering technique, and it exhibited superior HER activity compared to the Au catalyst without GBs. HER activity was inherently correlated with the density of the GBs in the Au catalyst, where active sites bind hydrogen more strongly. The possible reasons for this increase in H* binding ability were discussed, including geometrical and electronic features. The origin of the GB-assisted HER was the disorder of the atomic arrangement in the GB region on the Au surface, leading to the lack of complete coordination; thus, a strong H-Au bond formed to compensate for the lack of coordination. In addition, this disorder gave rise to the migration of the \(d\)-band center upward to the Fermi energy, leading to increased bonding. The GB-mediated HER performance emphasizes that the GB technique may be particularly suitable for applications in practical electrochemical hydrogen production.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12094290/s1](https://www.mdpi.com/article/10.3390/app12094290/s1)]([https://www.mdpi.com/article/10.3390/app12094290/s1](https://www.mdpi.com/article/10.3390/app12094290/s1)), Figure S1: Front and side views of fully relaxed periodic supercells for \(\bigcirc\)6[2-21] HAGB; Figure S2: SEM images of as-prepared (a) and annealed Au/CFP electrodes at 300 \({}^{\circ}\)C (c) and 400 \({}^{\circ}\)C (e). Compositional maps of as-prepared (b) and annealed Au/CFP electrodes at 300 \({}^{\circ}\)C (d) and 400 \({}^{\circ}\)C (f), with red indicating Au and green indicating carbon; Figure S3: X-ray diffraction patterns of Au/CFP for 30 s, 2 min and 5 min magnetron sputtering; Figure S4: Cyclic voltammograms under different scan rates for (a) Au/CFP, (b) Au/CFP\({}_{300}\) and (c) Au/CFP\({}_{400}\). (d) Electrochemically active (EA) surface area derived from a change in charging current density related to scan rate; Table S1: Calculated values for conversion of electronic energies to free energies. Assumed fugacities for gaseous H\({}_{2}\) are also included; Table S2: Calculated values for conversion of electronic energies to free energies on the GBs on Au(110) surface. Assumed fugacities for gaseous species are also included; Table S3: Calculated values for conversion of electronic energies to free energies of metals on (111) and (211) surfaces. Assumed fugacities for gaseous species are also included; Table S4: Calculated values for conversion of electronic energies to free energies of metals on (100) and (110) surfaces. Assumed fugacities for gaseous species are also included; Table S5: The flat surface and grain boundary active sites on Au(110). The coordination numbers and band centers are given.  
Data curation, formal analysis and writing--original draft preparation, R.J.; methodology and software, J.F.; supervision, Z.W.; supervision, funding acquisition and writing--review and editing, C.D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Natural Science Foundation of China (No.21403152) and Tianjin Natural Science Foundation (16)CQNJC05700).  
Not applicable.  
This study did not report any data.  
This study was supported by the Natural Science Foundation of China (No. 21403152) and the Tianjin Natural Science Foundation (16)CQNJC05700).  
The authors declare no conflict of interest.