Proposal
Electrochemical hydrogen evolution reaction (HER) is touted to be a sustainable energy conversion route. This reaction has been quite successful in acidic media due to the availability of protons but is challenging in alkaline reactions due to the lack of protons.1-3
Non-noble transition metals are known to be successful in catalyzing alkaline electrochemical HER. Their success stems from the generation of stable hydroxides in an alkaline environment, which creates a hydrophilic surface that aids water dissociation to free up protons for electrochemical HER. In addition, examples such as Ni provide a cost advantage of being inexpensive, and abundant compared to noble transition metals.4-6
Recently, studies have shown that metallic incorporation in metallic hydroxide layers has been shown to support electrochemical HER. For instance, Ni, Fe, Ag, and Pb co-precipitated in hydroxides have been shown to catalyze HER, and as a result, are important ions to look out for in reactions.7-9 In our study, the electrolyte used in HER is potassium hydroxide which has some degree of metallic impurity in it that can adsorb on the surface of these non-noble metals or possibly get inserted into the hydroxide structures. This process of metallic impurity adsorption or insertion into the metallic hydroxides can catalyze HER, leading to an overestimation of the catalytic performance of the metallic catalyst or their hydroxides. Consequently, we propose to evaluate the elemental profile of the potassium hydroxide to see if there are metallic impurities such as Fe, Ag, and Pb, that could influence the electrocatalysis of hydrogen production when Ni is used as a catalyst. In addition, some studies for reactions other than HER have shown that when Fe as an impurity is inserted into hydroxide layers, it causes the leaching of the metals originally in the hydroxide structure.10-12 The metal we intend to use for this study is Ni and therefore, we intend to evaluate the elemental profile of the potassium hydroxide for Ni to see if it Fe incorporation occurs which might induce leaching of Ni into the solution over time while the Fe is removed from solution over time.
In our supplementary project, our goal is to establish a working comparison of various Lewis acids and oxidant species to bring palladium into solution from palladium nanoparticles (NPs). This expands on work found by Hull et al. in which a palladium and iron co-catalyzed system was established for the aminoboration of terminal and internal unactivated alkenes.13 In this system, FeIII generated throughout the reaction from Fe(OTf)2 served to “leach” palladium back into solution, thereby re-activating the active catalyst. While Fe(OTf)2 provided the best oxidant for this purpose and product formation, establishing a comparison of various Lewis acidic additives and an organic oxidant. The Pd leaching study will indicate whether FeIII generated in the reaction is the most effective additive to bring Pd NPs into solution or a separate additive.14 Previous ICP-MS studies have only looked at the effect of Fe(OTf)2 and added chloride source, but other additives were shown to promote the aminoboration of norbornene in the catalytic study.
This investigation could provide key insight into additives that interact with palladium NPs to “re-activate” palladium catalyst. While the exact NP structure and surface interaction will need to be further investigated, this could provide potential impacts relating to catalyst recyclability.15 This is particularly desired in the case of palladium, which displays a propensity to form NPs from a homogeneous solution.16-18 These NPs can often display no reactivity, or otherwise reduced or undesired reactivity leading to unintended products. Furthermore, comparing these efficiencies to product yield could indicate any Lewis acids that interact with the NPs for turnover, but do not facilitate intended product.