| Fair Value Measurement | 
    | 7. | 
    FAIR VALUE MEASUREMENT  | 
 
 
  
Assumptions utilized in the valuation of Level 3 liabilities are
described as follows: 
  
    |   | 
      | 
    For the Three Months Ended | 
      | 
      | 
    For the Six Months Ended | 
      | 
 
    |   | 
      | 
    June 30, | 
      | 
      | 
    June 30, | 
      | 
 
    |   | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Risk-free interest rate | 
      | 
      | 
    0.16%-1.69 | 
    % | 
      | 
      | 
    1.88% - 2.45 | 
    % | 
      | 
      | 
    0.16%-1.69 | 
    % | 
      | 
      | 
    1.88% - 2.63 | 
    % | 
 
    | Contractual term (years) | 
      | 
      | 
    1.00-8.00 | 
      | 
      | 
      | 
    1.00 - 10.00 | 
      | 
      | 
      | 
    1.00-8.00 | 
      | 
      | 
      | 
    1.00 - 10.00 | 
      | 
 
    | Expected volatility | 
      | 
      | 
    93%-138 | 
    % | 
      | 
      | 
    106% - 139 | 
    % | 
      | 
      | 
    78%-138 | 
    % | 
      | 
      | 
    106% - 140 | 
    % | 
 
    | Expected dividend yield | 
      | 
      | 
    0.00 | 
    % | 
      | 
      | 
    0.00 | 
    % | 
      | 
      | 
    0.00 | 
    % | 
      | 
      | 
    0.00 | 
    % | 
 
 
  
The following table sets forth a summary of
the changes in the fair value of Level 3 warrant liabilities that are measured at fair value on a recurring basis: 
  
    | Warrants Payable | 
      | 
      | 
      | 
 
    | Beginning balance as of January 1, 2020 | 
      | 
    $ | 
    5,102 | 
      | 
 
    | Change in fair value of warrants payable | 
      | 
      | 
    16,039 | 
      | 
 
    | Ending balance as of June 30, 2020 | 
      | 
    $ | 
    21,141 | 
      | 
 
 
  
Assets and liabilities measured at fair value on a recurring or
nonrecurring basis are as follows: 
  
    |   | 
      | 
    June 30, 2020 | 
      | 
 
    |   | 
      | 
    Level 1 | 
      | 
      | 
    Level 2 | 
      | 
      | 
    Level 3 | 
      | 
      | 
    Total | 
      | 
 
    | Assets: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Alternative fuel credits | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    199,069 | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    199,069 | 
      | 
 
    | Marketable securities | 
      | 
      | 
    508,871 | 
      | 
      | 
      | 
    - | 
      | 
      | 
      | 
    - | 
      | 
      | 
      | 
    508,871 | 
      | 
 
    | Total assets | 
      | 
    $ | 
    508,871 | 
      | 
      | 
    $ | 
    199,069 | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    707,940 | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Liabilities: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Warrants payable | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    21,141 | 
      | 
      | 
    $ | 
    21,141 | 
      | 
 
    | Total liabilities | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    21,141 | 
      | 
      | 
    $ | 
    21,141 | 
      | 
 
 
  
    |   | 
      | 
    December 31, 2019 | 
      | 
 
    |   | 
      | 
    Level 1 | 
      | 
      | 
    Level 2 | 
      | 
      | 
    Level 3 | 
      | 
      | 
    Total | 
      | 
 
    | Assets: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Alternative fuel credits | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    476,992 | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    476,992 | 
      | 
 
    | Marketable securities | 
      | 
      | 
    3,150,332 | 
      | 
      | 
      | 
    - | 
      | 
      | 
      | 
    - | 
      | 
      | 
      | 
    3,150,332 | 
      | 
 
    | Total assets | 
      | 
    $ | 
    3,150,332 | 
      | 
      | 
    $ | 
    476,992 | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    3,627,324 | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Liabilities: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Warrants payable | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    5,102 | 
      | 
      | 
    $ | 
    5,102 | 
      | 
 
    | Total liabilities | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    5,102 | 
      | 
      | 
    $ | 
    5,102 | 
      | 
 
 
 |