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Mechanical energy derived from friction is a kind of clean energy which is ubiquitous in nature. In this research, two-dimensional graphite carbon nitride (g-C3N4) is successfully applied to the conversion of nitrogen (N2) fixation through collecting the mechanical energy generated from the friction between a g-C3N4 catalyst and a stirring rod. At the stirring speed of 1000 r/min, the tribocatalytic ammonia radical (NH4+) generation rate of g-C3N4 can achieve 100.56 μmol·L−1·g−1·h−1 using methanol as a positive charge scavenger, which is 3.91 times higher than that without any scavengers. Meanwhile, ammonia is not generated without a catalyst or contact between the g-C3N4 catalyst and the stirring rod. The tribocatalytic effect originates from the friction between the g-C3N4 catalyst and the stirring rod which results in the charges transfer crossing the contact interface, then the positive and negative charges remain on the catalyst and the stirring rod respectively, which can further react with the substance dissolved in the reaction solution to achieve the conversion of N2 to ammonia. The effects of number and stirring speed of the rods on the performance of g-C3N4 tribocatalytic N2 fixation are further investigated. This excellent and efficient tribocatalysis can provide a potential avenue towards harvesting the mechanical energy in a natural environment.

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Piezo-electrocatalysis based on the non-centrosymmetric materials opens an avenue for mechano-to-H2 production through harvesting mechanical energy, being undergoing significant growth. Direct comparison of the performance of various piezo-electrocatalysts is necessary to obtain the optimal candidates for satisfying the demands of practical application but remains a grand challenge because the acquiescently added sacrificial agents vary considerably in the literature. Herein, we systematically investigate the effect of four commonly used types containing totally 15 sacrificial agents on the piezo-electrocatalytic hydrogen evolution by choosing the typical BaTiO3 catalyst as the demo. It is found that the pH, length of the carbon chain, adsorption strength between catalysts and sacrificial agent, and combination of sacrificial agents would impact on the piezo-electrocatalytic H2 evolution performance. Moreover, the self-decomposition effect is found in the sacrificial agent-water mixtures under ultrasonic vibration, implying that H2 can be generated without piezo-electrocatalysts, which was usually ignored. Thus, in this work, a concept of net H2 yield is suggested to standardize the evaluation of piezo-electrocatalysts in future.