Nitrogen-Doped Nanoporous Carbon Membranes with Co/CoP Janus-Type Nanocrystals as Hydrogen Evolution Electrode in Both Acidic and Alkaline Environments

Identifying and building a sustainable energy system are perhaps two of the most critical issues that today's society must address. Replacing our current energy carrier mix with a sustainable fuel is one of the key pieces in that system. Hydrogen as an energy carrier, primarily derived from water, can address issues of sustainability, environmental emissions, and energy security. Issues relating to hydrogen production pathways are addressed here. Future energy systems require money and energy to build. Given that the United States has a finite supply of both, hard decisions must be made about the path forward, and this path must be followed with a sustained and focused effort.

While platinum has hitherto been the element of choice for catalysing oxygen electroreduction in acidic polymer fuel cells, tremendous progress has been reported for pyrolysed Fe-N-C materials. However, the structure of their active sites has remained elusive, delaying further advance. Here, we synthesized Fe-N-C materials quasi-free of crystallographic iron structures after argon or ammonia pyrolysis. These materials exhibit nearly identical Mössbauer spectra and identical X-ray absorption near-edge spectroscopy (XANES) spectra, revealing the same Fe-centred moieties. However, the much higher activity and basicity of NH3-pyrolysed Fe-N-C materials demonstrates that the turnover frequency of Fe-centred moieties depends on the physico-chemical properties of the support. Following a thorough XANES analysis, the detailed structures of two FeN4 porphyrinic architectures with different O2 adsorption modes were then identified. These porphyrinic moieties are not easily integrated in graphene sheets, in contrast with Fe-centred moieties assumed hitherto for pyrolysed Fe-N-C materials. These new insights open the path to bottom-up synthesis approaches and studies on site-support interactions.