This Small Business Innovation Research Phase II project will further develop the nitrogen gas absorbing organic-metallic liquid absorbents, called NiSorb liquids, and the NiSorb heat pumps to be more compact, environmentally clean, and up to 70% more efficient than current systems. Reversible absorption/desorption of nitrogen gas refrigerant was demonstrated in Phase I verifying the feasibility of the concept. The research will optimize the NiSorb liquids to have the thermophysical properties that give maximum heat pump efficiency. The analytical model from Phase I will be further developed so it can be used to determine ideal thermophysical properties and design heat pumps. Larger quantities of NiSorb liquid will be made and methods for large-scale production will be developed with assistance from a large chemical manufacturing company. A prototype NiSorb heat pump will be designed, built and tested and its performance compared to that of other competitive heat pumps. A chemical manufacturing company will be identified to manufacture the NiSorb liquids and a heat pump manufacturing company will be identified to manufacture the NiSorb heat pumps in Phase III. Two Phase III Follow-On- Funding commitments have been obtained. The environmentally clean NiSorb heat pump with the efficiency of 70% higher than current systems is deal for residential and commercial heat pumps, air conditioners, refrigerators, ice makers, electronic coolers, process heating and cooling and similar applications. Cryogenic cooling is also possible with special liquid absorbent formulations and Joule-Thompson expansion of cold gas. If this more efficient technology were fully implemented in the US the energy saving would be approximately 9.5 Quads or nearly 12.4% of US energy consumption.