The facile decomposition of ammonia to produce hydrogen is critical to its use as a hydrogen storage medium in a hydrogen economy, and although ruthenium shows good activity for catalysing this process, its expense and scarcity are prohibitive to large-scale commercialization. The need to develop alternative catalysts has been addressed here, using microkinetic modelling combined with density functional studies to identify suitable monolayer bimetallic (surface or subsurface) catalysts based on nitrogen binding energies. The Ni-Pt-Pt(111) surface, with one monolayer of Ni atoms residing on a Pt(111) substrate, was predicted to be a catalytically active surface. This was verified using temperature-programmed desorption and high-resolution electron energy loss spectroscopy experiments. The results reported here provide a framework for complex catalyst discovery. They also demonstrate the critical importance of combining theoretical and experimental approaches for identifying desirable monolayer bimetallic systems when the surface properties are not a linear function of the parent metals.

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Atomic layer deposition (ALD) was utilized as a synthesis method to deposit monolayers of Pt onto WC substrates for applications as oxygen reduction reaction electrocatalysts. Samples utilizing various Pt ALD cycles were characterized using surface analytical methods and scanning electron microscopy, whereas cyclic voltammetry was used to determine whether the oxygen reduction reaction takes place on the catalyst surface. ALD Pt was found to deposit onto WC substrates following an island growth mechanism. When few Pt ALD cycles are used, discrete Pt particles first formed and dispersed over the WC substrate, but at least 100 ALD cycles is required for the WC substrate to be covered with Pt. Whereas Pt monolayers are not obtained, ALD Pt on WC still shows activity for the oxygen reduction reaction. Cyclic voltammetry conducted in an O 2 -saturated 0.5 M H 2 SO 4 electrolyte indicate that as few as 20 Pt ALD cycles on WC is needed to produce oxygen reduction reaction activity that is comparable to Pt bulk. Efforts to make Pt films that are even thinner and more monolayer-like are desired, and potential approaches are discussed.

Selective reforming of biomass-derived oxygenates to produce hydrogen or syngas (H 2 þ CO) offers an attractive route for biomass utilization. As reported previously, the Ni/Pt(111) bimetallic surface, with one monolayer of Ni residing on top of Pt(111), showed enhanced activity in oxygenate reforming. However, the Ni/Pt(111) structure is not stable at high temperatures because of diffusion of Ni into bulk Pt. In the current study we explore the possibility of replacing the Pt substrate with tungsten monocarbide (WC) to prevent the diffusion of monolayer Ni into the bulk. We report a combined study using density functional theory (DFT), temperature programmed desorption (TPD), and high resolution electron energy loss spectroscopy (HREELS) to compare the reforming reaction of ethanol on Ni/Pt and Ni/ WC surfaces. Strong similarities are observed in the reaction pathways of ethanol on monolayer Ni/Pt and Ni/WC, demonstrating the feasibility to replace Pt with WC and to use monolayer Ni/WC as active and less expensive reforming catalysts.

We investigate the decomposition of ammonia on bimetallic surfaces prepared by the deposition of a monolayer of Fe, Co, or Cu on a Pt(111) surface computationally and experimentally. We explore the correlation between predicted activities based on the nitrogen binding energies with experimental decomposition activity on these bimetallic and corresponding monometallic surfaces. Through density functional theory calculations and microkinetic modeling, it is predicted that the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces, with a monolayer of Fe or Co on top of Pt(111), are active toward decomposing ammonia. In contrast, the corresponding subsurface configurations, Pt-Fe-Pt(111) and Pt-Co-Pt(111) are inactive. These predictions were confirmed experimentally through temperature programmed desorption experiments. Decomposition was seen at temperatures below 350 K for the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces. For the Cu∕Pt(111) system, the surface, subsurface and parent metals were each predicted to be inactive, consistent with experiments, further validating the model predictions. The stability of these bimetallic surfaces in the presence of adsorbed nitrogen is also discussed.