  The hydrogen evolution reaction (HER) is a key process in electrochemical
water splitting. To lower the cost and environmental impact of this process, it
is highly motivated to develop electrocatalysts with low or no content of noble
metals. Here we report on a novel and ingenious synthesis of hybrid PtxNi1-x
electrocatalysts in the form of a nanoparticle-necklace structure named
nanotrusses, with very low noble metal content. The nanotruss structure
possesses important features, such as good conductivity, high surface area,
strong interlinking and substrate adhesion, which renders for an excellent HER
activity. Specifically, the best performing Pt0.05Ni0.95 sample, demonstrates a
Tafel slope of 30 mV dec-1 in 0.5 M H2SO4, and an overpotential of 20 mV at a
current density of 10 mA cm-2 with high stability. The impressive catalytic
performance is further rationalized in a theoretical study, which provides
insight into the mechanism for how such small platinum content can allow for
close-to-optimal adsorption energies for hydrogen.
