The hydrogen evolution reaction is quite simple:
2 H+ + 2 e−→ H2
It describes two hydrogen ions receiving the electrons to turn them back into regular hydrogen. What is missing from my version of the equation above is the state symbols which would help show where this interaction happens. The hydrons (positive hydrogen ions) should have an aqueous symbol to show they’re dissolved and the hydrogen that is released is given off as a gas. When water is split by electrolysis it’s the dissolved hydrons which turn into hydrogen in this way. The electrolysis of water is considered quite an energy and time consuming way of getting hydrogen, especially if it is attempted without a catalyst; and it is these catalysts that today’s paper is about.
One catalyst that has been shown to be effective recently is molybdenum disulphide (MoS2) in the form of nanoparticles or an incredibly thin sheet. Now, like with many of the transition metal dichalcogenides, MoS2 has many different phases which are unlocked under various temperatures and pressures. Rather than the common one of interest, the superconducting phase, the main difference in the catalytic ability is between the metallic and semiconducting phases. The metallic phase, 1T-MoS2, has much more potential than the semiconducting version but this activity comes with the downside of being harder to produce with greater hindering from the ambient conditions.
It has also been predicted that tantalum sulphide (TaS2) should also show the electrocatalytic with significantly more stability. A study was performed which showed this prediction to be correct but that 1T-TaS2 couldn’t match 1T-MoS2‘s abilities possibly due to an increased oxidation rate which could block some of the tantalum sulphide’s active sites. In order to see if this problem could be circumvented low pressure formation of TaS2 thin films was attempted on aluminium foil resulting in 2H-TaS2. The effectiveness of the catalysts produced in the hydrogen evolution reaction was very good, on a similar level to that of platinum (which is considered one of the best despite being very expensive). The production method suggested should hopefully find applications in making more 2D metallic catalysts in the future.