As observed in Figure , high faradaic efficiencies (FE) of up to 100% for the HER were obtained for both samples as quantified with gas chromatography. [Mo3S13] 2-showed a FE of 103±7% (Table ) after 10 minutes of 1 sun illumination at an applied potential of -0.2 V versus RHE. Under the same conditions, [Mo3S4] 4+ showed varying values with an average FE of 88±17% (Table ). The larger error for the GC measurements with [Mo3S4] 4+ likely results from the lower photocurrent and, therefore, the longer time for the mass transport of hydrogen from the solution to the headspace, where it can be measured by GC.