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Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

This article presented a new type of stick-slip piezoelectric actuator based on an asymmetrical flexure hinge driving mechanism. The key of the driving mechanism was a four-bar mechanism with different minimum thicknesses of right-circle flexure hinges. Combined with a symmetrical indenter, the asymmetrical flexure hinge driving mechanism generated controllable tangential displacement by changing the locking force. Therefore, the simple structured stick-slip piezoelectric actuator achieved considerable improvements especially in output speed and efficiency. In order to obtain improved actuator properties, the minimum thicknesses of asymmetrical flexure hinge driving mechanism, the tangential and normal displacements of the indenter were analyzed and investigated by finite element method. A prototype was fabricated and experiment investigation of the actuator characteristics was presented. Testing results indicated that the actuator achieved the maximum velocity of 15.04 mm/s and its maximum load reached 440 g under a voltage of 100 Vp-p and a frequency of 490 Hz. The maximum efficiency of the actuator was 3.66% with a load of 280 g under a locking force of 5 N and the actuated velocity of 10.17 mm/s.