Electrocatalytic hydrogen evolution reaction (HER) has been intensively studied. Materials innovation and device engineering for HER has been focused on both acidic and alkaline systems, for which great progress has been made. However, there has been very limited studies for neutral solution. Generating H₂ from water of intermediate pH (e.g., wastewater, seawater) has advantages of being less corrosive, environmentally benign, and potentially low cost. It also provides an efficient way for environmental cleanup, for example, H₂ production using a microbial electrolysis cell (MEC) cleans wastewater. HER electrocatalysts based on earth abundant materials for operation in neutral conditions, which has been rarely explored, is thus highly attractive but remains a grand challenge.

Here we report our recent materials research and fundamental understanding on HER electrocatalysis in neutral solution. We have developed a new pseudo in situ synthesis method for the preparation of HER electrocatalysts molybdenum phosphide (MoP). The surface structure and chemistry can be easily controlled which enables us to study the structure-property relationship. Our MoP electrocatalyst demonstrates HER activity comparable to that of benchmark Pt in neutral solutions including natural sea water and phosphate buffered saline solution. It also demonstrates high stability with no performance fading in 4000 cycles. MoP electrocatalyst was further tested in an MEC, which is able to produce a 2X HER current density in comparison to the state-of-art MEC in literature. The high performance MEC with the new HER catalyst presents a promising technology approach for low cost hydrogen production.